|CERES No. 121 (FAO Ceres, 1988, 50 p.)|
Before agricultural reform began to sweep rural China, fresh vegetables at reasonable prices were hard to find, especially for the country's 200 million city dwellers.
Today, farmers who used to grow grains and vegetables according to central plans created by government bureaucrats are free to choose what to grow and where to market it. Increasingly, rural entrepreneurs are shuttling between villages and cities to bargain at wholesale and retail markets. Crop diversification - away from basic grains - and a liberalization of marketing controls are making the Chinese rural economy boom.
At the Beijing Vegetable Research Centre, on the outskirts of the capital, dozens of China's leading botanical scientists work to ensure that the vegetables reaching urban rice bowls are the freshest, most nutritious, palatable, and attractive that nature can provide. As with many other aspects of applied plant research and technology in China today, outside experience and scientific expertise are needed to help achieve this goal.
Staff members of Beijing Research Centre carefully monitor the growth of more than 100 varieties of hybrid vegetables
Picking her way carefully through a field of almost 100 varieties of broccoli from around the world, Chen Hang, the Centre's Director, explains, "Before the reforms and the launching of our research programme, vegetable crop losses were often as high as 50 per cent and quality was inconsistent. Here we concentrate on developing varieties that are disease and weather resistant, on ensuring good seed and improving post-harvest storage, and on basic extension and training for a growing number of farmers throughout China."
Government agencies in charge of vegetable production used to issue orders to communal organizations, but new they provide individual farmers and cooperatives with suggestions, loans, and economic and technical information based, in large part, on what is being tried at the Centre. As a result, the total area planted in vegetables around 33 big cities is growing at almost 10 per cent a year. The vegetable trade volume at the country's urban free markets now surpasses that in government-run retail shops.
The Centre's researchers are giving top priority to developing vegetables that withstand higher and lower temperatures and that are disease- and pest-resistant. They are now breeding new types of tomatoes resistant to virosis and late blight; cucumbers
resistant to downy mildew and soft rot; and eggplants resistant to verticillium wilt and parasitica Dast. Work is also under way on cold-resistant spinach and cucumber, and on heat-resistant and non-waterlogging tomatoes.
Such experiments require more than simple introduction of other varieties from China or abroad. It is essential, instead, to apply plant breeding experiences from abroad to local conditions throughout the country. Such international technical transfer of on-site research and development is being sponsored through a $680 000 grant from the United Nations Development Programme (UNDP), the world's largest multilateral source of grants for technical aid to the developing world.
Under an arrangement worked out in 1979 between UNDP and the Beijing Academy of Agricultural Sciences, the Vegetable Research Centre is being strengthened in
China's top botanists are aiming for disease- and weather resistance, good seeds, and improved post-harvest storage several different ways. For example, Chinese researchers were sent to Europe and the United States for a period of ten months to study breeding and post-harvest physiology. A 40 per cent increase in output of Chinese cabbage, a mainstay of the country's diet, is attributed to the knowledge acquired by one of the Centre's researchers during a stay of several months in California, and 60 per cent of total production is now in the improved variety."
Foreign experts also come directly to the Centre to provide technical training and consultation on equipment purchasing for new laboratories. One eminent vegetable breeder came to help set up facilities for analyzing post-harvest physiology. Another brought expertise in the use of climate chambers and physiological analysis of the soil. Foreign exchange provided by UNDP goes to purchase new foreign-made equipment, and the Government provides the local funds to purchase land for experimental plots.
The four-hectare breeding farm surrounding the Centre is like a garden of Eden. Almost 100 types of fruits and vegetables and a wide variety of flowers are carefully nurtured under China's powerful summer son. Under protection of plastic covered greenhouses, special breeds of green peppers and eggplants are cross-bred to develop the variety best suited to a certain growing season in some particular part of China.
The Centre also invites cooperative- and county-level extension people to visit and learn about its innovations, and some 24 000 people have already trained there.
The application of modern technology and the introduction of free markets is serving to boost rural incomes in rural China and, at the same time, to serve better the needs of an increasingly consumer-oriented urban population. But the process of Chinese agricultural modernization is only beginning. "We love and respect nature," says Chen, "but now we're beginning to work hard on frozen vegetables."
Mali, like most African countries, imports 100 per cent of its paper, but it is one of the world's poorest countries. These imports drain a large portion of its very limited foreign currency reserves and thus constitute a serious handicap for the country's schools, literacy training, and publishing.
But how can Mali possibly produce its own paper? In other African countries, such as Nigeria and Cameroon, paper-making from wood pulp devours energy, is a tremendous water and air pollutant, and has devastated the countries' forests. In view of these disastrous consequences in humid equatorial regions, a paper industry in a Sahelian country overcome by drought and desertification seems inconceivable.
Against all odds, the National Research Institute for Stockraising, Forestry, and Hydrobiology at Bamako, the capital city, has a "paper workshop" where engineers are experimenting with paper-making from alternative raw materials, trying different technologies.
Non-woody plant matter, such as gumbo, "dah" (or kenaf), banana tree, jute, bagasse, or cotton stalks, offer interesting possibilities. In a country whose largest export crop is cotton, cotton stalks, considered plant residue, could represent an additional source of income for producers. Every year, Malian farmers burn or bury more than 200 000 metric tons of cotton stalks; unlike millet or maize stalks, cotton stalks cannot be used for animal feed.
Mr Ousmane Samassu, a member of the Forestry Commission who for many years has been taking part in the research, tried to grind millet stalks in two experimental workshops at Zangasso and Fonfana in the cotton-producing regions of Su and Sikasso, but the process proved too long, too difficult, and too unprofitable.
He was not discouraged. As a member of AMADE, a Malian NGO for development with close links to CIMADE, he turned to the North-South Foundation in Paris where he obtained a grant which enabled him to continue his research on paper making from plant residues and non woody matter at the Tropical Forestry Technical Centre (CTFT) at Nogent sur Marne, in France.
A trip to India offered promise for South-South cooperation. Indeed, India's numerous small-scale paper mills are using non-woody products as raw materials: jute stalks, sugar cane fibre, and rags, requiring simple techniques and abundant unskilled labour. Five per cent of the country's paper consumption is produced in this way. A small mill can produce 200-1 500 kg of paper a day.
The manufacture of paper from cotton stalks has the advantage of causing hardly any pollution and requiring very little water. This is important in a country like Mali, where the climate is uncertain.
The paper-making process is semi-mechanized: operations such as crushing and pressing can be done manually. The basic equipment is a hydraulic press, which may be accompanied by a shredder, a digester, and a grinder.
The paper thus produced is stronger than that obtained from wood pulp. Its only drawback is its rather less clean appearance.
Since June 1987, Mr Samassu, with the support of AMADE and the Implementation and Technological Exchange Group, Paris, has been applying the results of his research in Mali. His new paper workshop at Bamako will initially be used for demonstration purposes, aiming at producing 50 tons of paper a year. A small-scale project, this experiment will be used as an incentive to develop small decentralized paper-manufacturing units.
In parallel with paper production and marketing, Mr Samassu insists on continuing his research on high-yield methano-chemical paper pulps, using soda, lime potash, and ammonia. So far, although soda and lime are the most efficient, potash and ammonia leave residues that can be used as fertilisers. And potash, which is almost completely assimilated, causes no pollution. Before making a final choice, a consumption record will be compiled for each chemical used.
Naturally, important financial investments are required for the equipment. The EEC, the World Bank, and UNIDO have already been contacted. Mr Samassu also favours cooperation between India and Mali. With this in view, an agreement has been signed by AMADE and a New Delhi NGO, the Society for Development Alternatives, marking the beginning of South-South cooperation for small-scale paper production units.
However, Mr Samassu is aware of the difficulties of his project, particularly with regard to marketing and distribution. In its first year the workshop will produce cartons, cardboard boxes, and cardboard folders. The market already exists: from 1963 to 1980 paper and cardboard box consumption increased by 70 per cent. Since then, the industry has been seeking reliable clients: the Government; EDIM (Mali's largest printers), SOMOPAC (the major packaging industry), and joint ventures. It must also diversify its production and become flexible enough to meet new demands for writing paper, egg cartons, fruit containers, thick cardboard doors, and partitions.
Once it has been proved that the creation of a small paper industry is a viable proposition in a Sahelian country, the experiment will bring new hope to the Sahel and even to the whole of West Africa, where, as yet, there is no paper industry.
In the Dalifort quarter on the outskirts of Dakar, one of the city's most precarious neighbourhoods, a shantytown with a very mixed population, a group of women have gone into the fish business. They retail fresh fish which they have bought in other markets farther away. A French sociologist, Mireille Lecarme, followed the progress of this experiment and studied the mobile and lively milieu in which old peasant women or vegetable vendors have come in from the country to become retailers of carp, mullet, morays, and sardines.
Even if, as they say, "the sea of Dakar is not for them," the rural women who no longer live on the land their ancestors left them deploy prodigious organization to exploit the sea's wealth as they do. They spare the neighbourhood customer at least three kilometres of travel to the nearest market, that at Hann, and longer trips to other markets. They women shuttle back and forth, sometimes on foot, carrying their full baskets on their heads, but more often they make deals with a number of drivers and go by bus.
The best off among them go to the large market at la Gueule Tap which, though farther from Dalifort than Hann, offers a larger choice of fish. There they follow their purchases with an almost ritual daily breakfast, and in this they follow the example of their male "colleagues".
Lecarme stresses the special features of the women's market of Dalifort: brutal price fluctuations that make prediction impossible and the exigencies of a clientele with very little money to spend. The latter forces the women retailers to lower their profit margin considerably. "More than one of them", she says, "feels relieved when she merely breaks even."
She also insists upon the preeminence of the social factor over the economic factor: "The objective competition present is attenuated by a cluster of daily social practices: gestures, gifts, words, laughs, care of children, dances." The market thus constitutes "a paradoxical place where two social modalities meet: the older goes back to a system of barter, to the "teranga" essential value based on the sense of collectivity, exchanges of gifts which has stayed with the women; the second, the product of colonization and of monetization, poses the primacy of the individual and subordinates the social to the quest for individual gain. Marketing plays on these two modalities: the vendor will lower her prices only by steps, in function of the market and not because of the customer's bargaining skill. On the contrary, she will simply give away fish to a relative or woman friend."
Ethnic differences govern choice of vendor and choice of fish: "Women customers prefer to go to a vendor of their own ethnic group for the pleasure of speaking their own language and choosing fish that are to their own taste; for the Kiola that means ouass and quiss, carp and mullet, for the Toucouleurs it is sompet, which carp, and pageots."
The spontaneous and improvised nature of the vendors' organization in this shantytown has not stood in the way of the development of a hierarchy. Lecarme distinguishes between the "bigs" who benefit at the outset from greater capital and do their best to procure fine fish for a clientele that can provide secure profits, and the "smalls" who buy mostly "yabol" (sardines) on the beach at Hann and need supplementary activities (such as the sale of fruit or the clandestine sale of drink), "which presupposes the access to credit at usury rates, a rotation of debts, the help of the husband or of a relative of her own." Savings clubs permit daily saving, and this system too closely unites the local and the economic sides of life.
To conclude her report, Lecarme recalls "the need to think of development in the feminine, as well as in the masculine, in its social implications as well as in its economic". In her opinion, it would be disastrous, for example, to implement a project that has been proposed by the CAPAS (Senegalese centre for assistance to artisanal fisheries) which addresses only fishermen members of cooperatives of provisioning the marketing of their fish, in suppressing "external intervenors" as the women of Dalifort. ''If this project were implemented across the board," she says, "it is probable that a good number of families would see their standard of living fall below the tolerable level.
Around 650 B.C. one Ali Yanouf is believed to have built a dam, some twelve metres high, at Marib in Yemen. Today, just 3 km upstream stands a wall 38 metres high, 227 metres long at the bottom, and 763 metres at the top, barring the course of Wadi Abida at the exit of the gorges of the Djebel Bilak. Ali Yanouf would be proud that the modern behemoth was merely bringing up to date one of his ideas, considered quite daring in their own day.
At some 120 km from San 'a, capital of the Yemen Arab Republic, Marib is situated in a region of high plateau. This is the heart of what, in the first millennium B.C., was the opulent, and already irrigated, land of Sheba, whose queen took King Solomon a gift of "an hundred and twenty talents of gold, and of spices very great store, and precious stones", and asked him "hard questions".
But such wealth is, well, ancient history. Yemen today is one of the poorest countries in the world and was long one of the most stagnant. Its economic situation may be described succinctly with the aid of some indicators of its poverty. Its population growth is too rapid (a rate of 2.8 per cent has brought the population to more than 9 million in 1986, and this rate is expected to exceed 3 per cent between 1980 and 1990); the concept of hygiene is still in its infancy; teaching could be more developed; inflation is galloping; emigrant workers supply labour to all the Gulf States and support their families with their remittances; the balance of payments deficit is astronomical, the amount of imports of food products alone being more than eight times higher than the total value of the country's exports.
Measures to allow the country to attain a degree of self-sufficiency in food were urgently needed. Agriculture was, accordingly, promoted energetically, and the keystone of the new agricultural policy established by the 1987-91 Plan is the development of irrigation.
The Marib dam, begun in 1984, was inaugurated in 1987. Financing of $75 million supplied by the Abu Dhabi Fund for Arab Economic Development covers the building of the dam proper plus the deepening of a 40-km main canal and 10 km of primary canals. Construction was done by a Turkish company. The dam holds back the waters of an artificial lake with a volume of 398 million m3 and a surface of 30.5 km2 the product of flooding the valley of a catchment basin of 10 000 km2. In a first phase, irrigation will extend to 6 340 hectares. In a second phase, still under study, the construction of new works of drainage will double the present area and bring the irrigated surface to 12 000 hectares. Costs are estimated at $30 million.
The new lands thus acquired by irrigation will grow wheat, citrus fruit, green vegetables and vines for table grapes, all for the domestic market. Some "hard questions" still remain, and their solution requires the wisdom of a Solomon. The price of the water and its mode of recovery, for example, are not yet known and nobody is saying anything about how the irrigated areas will be farmed. There are appalling problems of land tenure, since Colonel Saleh's government has not chosen virgin lands to make more productive but territories possessed by rather restless tribes and already being farmed by small producers who have practised irrigation for generations - small-scale artisanal irrigation, of course, by extending the floods (a practice called seil locally) or boreholes or both. This is how 3 301 hectares are still irrigated, since the dam is not yet operational. The farms are intensively cultivated with wheat, barley, sesame, maize, lucerne, legumes, and fruit trees.
Animal husbandry also occupies an important place in the current farming systems and represents an important contribution to income for farms irrigated by boreholes or by a combination of boreholes and seil, and accounts for most of the incomes of those farms irrigated only by seil.
The hydrologists who have studied the zone estimate that these farm level irrigation methods are satisfactory given the present state of affairs. And indeed the possibility of simply continuing as in the past has been considered. But those methods have their limits. The first is the unpredictability of the harvests, the second the damage caused by flooding, the third the accelerated progression of boreholes: recharging the ground water could bring problems in the not too distant future. Finally, the fourth and most compelling limit is that the irrigation systems used till now permits neither increasing productivity nor putting more land under cultivation.
The system should permit six irrigations per growing season, which will involve significant changes in the present situation. Cultivation of sorghum, for example, will be effectively eliminated; this grain needs only one irrigation per season, and continuing to grow it would involve a waste of very costly water. Not only will growing systems be upset, but newly irrigated lands will have to be redistributed. And a number of legal battles over property lines are already in progress.
As attractive as the prospect of not having to import 600 000-650 000 metric tons of wheat and wheat flour every year from Australia, the US, the EEC, Canada, and even Saudi Arabia (imports of 16 000 tons from these countries is foreseen for 1988) may be, the Arab Republic of Yemen needs more than self-sufficiency in food to offset its trade balance deficit. It must reduce imports but also step up exports. In the very near future, Yemen counts on taking advantage of a new resource and joining the oil-exporting countries. One of the many sites surveyed, Alif, is ready to be exploited. The figures advanced on the petroleum reserves of the country are still rough and fluctuate between 300 and 500 million barrels. New prospecting is being done in the Red Sea and in the centre of the country. Exports will begin when construction of the 430 kilometre oil pipeline to link Alif to Salif, on the coast, has been completed, probably in November. Oil revenues which, according to some estimates, could rise to $2.5 billion, would be, for the first time in the world, absorbed in large part into agriculture.
"Four or five tortillas, an avocado, and a cup of coffee - that's a good meal." So say the Indians of Guatemala. And they're right. The dark-green pear-shaped fruit, the avocado, is a popular food in Central America and an extremely nutritious one. Not to mention appetizing; cheap, and available throughout most of the year.
It contains between 9 and 30 per cent oil similar in composition to olive oil, as well as high quantities of vitamin B. Experiments at the University of California have shown that the digestibility of avocado fat is equal to that of butter fat and not below that of beef fat. Since avocados are rich in oil, they also provide calories, 123 to 387 per 100 grams of avocado pulp.
But they are low in sugar - only about I per cent - which means that the fruit is recommended as a high energy food for diabetics.
The avocado gives a relatively high content (1.0-1.4 per cent) of iron-rich ash. Experiments have demonstrated that anaemic rats formed haemoglobin when fed diets supplemented with 1-5 grams of avocado pulp. Since avocado iron is physiologically available, it should be a valuable dietary factor in the prevention or cure of anaemia.
The total dry matter in the edible portion of the avocado is, at 30 per cent, greater than in any other fresh fruit. (The nearest contender, the banana, contains only 25 per cent.) The avocado also outdoes other fresh fruits in content of mineral matter. Soda, potash, magnesium, and lime account for more than half the ash or mineral matter. For protein and ash, the avocado surpasses any other fruit, and it contains on average fully 50 per cent of the carbohydrates contained in many fresh fruits.
For many Central Americans, the avocado takes the place of meat in the diet. When meat is scarce, the fact that an acre of land will yield a larger amount of food if planted to avocados than it will with any other tree crop assures the continued importance of the avocado industry in Latin American and Caribbean countries. That region's regular suppliers of the international market include the French overseas department of Martinique, Mexico, Guatemala, the Dominican Republic, and Peru. Demand is increasing significantly as a result of the development of new domestic and export markets. In the USA alone, the volume of avocados sold on the domestic market has increased tremendously. In Western Europe, imports of the fruit have also increased remarkably. France is by far the leading importer followed at a long distance by the United Kingdom. The two countries account for about 70 per cent of the total imports and are also largely responsible for the rapid rise in imports in recent years. Other European importers include Belgium, Denmark, Italy, the Netherlands, Finland, Norway, Sweden, Austria, and Switzerland.
The major suppliers to the Western European countries have so far been Israel and the Republic of South Africa. However, future exports from these countries will be facing tough competition not only from the Latin American and Caribbean countries but also from African countries, especially Kenya, Cameroon, and Cd'Ivoire.
Recipes for tasty avocado dishes abound. A purof avocado, lime juice, salad dressing, and salt is suitable for freezing. An avocado salad base can be prepared by blending 100 parts avocado with five parts lemon juice, four parts chopped onion, and one part salt.
In Brazil, where the avocado is regarded more as a dessert than as a staple foodstuff, it is made into a delicious ice cream. Avocado cookbooks have been published in Cuba, and in the avocado-growing states of Florida, California, and Hawaii in the USA.
Avocado trees, broad-leaved evergreens of the family Lauraceae, genus Persea, can be grown in all tropical and subtropical areas. In general they require the same growing conditions as citrus fruit but need more water. There are three recognized races of avocados based on their ecological origin - Mexican, Guatemalan, and West Indian. The Mexican race is native to the mountains of Mexico and Central America. The Guatamalan originated from the highlands of Central America. The West Indian race is native to the lowlands of Central America and northern South America. Many cultivars of commercial importance are hybrids of these three races.
The primary means of transporting avocados to the various markets is by truck within the country of origin and by ship for export. Only a small proportion of the avocados in international trade travel by air. Kenya is one exception that air-freights its avocados, but supplies from most other countries go by sea. For long distance shipments controlled-atmosphere containers are used which allow fruit to arrive in excellent condition, even after long sea voyages.
The fruits are picked and shipped when they are mature but firm and thus require ripening prior to consumption. The temperature at which an avocado is ripened has a pronounced effect on the rate of ripening and the quality of the ripened fruit in terms of flavour, texture, and appearance.
The avocado fruit is unusual in that it need not be picked as soon as it reaches maturity. In California, some cultivars can remain on the tree for six months or longer after maturing. Florida-grown cultivars can remain on the tree for as little as three weeks or for as long as three months after maturing. Generally, fruit of the summer cultivars belonging to the West Indian race remain attached to the tree for shorter periods of time than the later maturing cultivars. Shipping of fruits which have reached maximum maturity is not recommended because their shelf-life is reduced and their large seeds may sprout.
To make cold using heat: that is the challenge that a French company has accepted. It has perfected and manufactured a refrigerator with no moving parts, which needs no maintenance, and which makes ice using the heat of the sun as its only source of energy.
This simple-looking "product" is actually the result of several years of work on the phenomenon of adsorption, the principle, in physics, of the taking up of a gas or a liquid at the surface of a solid. The refrigerator has been nicknamed "Gaspard", which stands for (in French) Solar Adsorption Generator for the Independent Production of Soft Refrigeration.
Seen from outside, Gaspard resembles an ordinary refrigerator with a solar heat collector on top. But there is nothing ordinary about its innards. There is no electric motor or compressor to produce the cycle of alternating liquid and gas phases of a fluid that produces cold by evaporation. Instead the sun does all the work. The alternation of evaporation and condensation follows the rhythm of day and night between a condenser placed under the solar collector and an evaporator in the body of the refrigerator
The condenser contains activated carbon, that is, grains of carbon whose microscopic pores have been created by thermal shock, by heating them to 500-600 degrees centigrade, so that the grains become riddled with microscopic pores. A gram of carbon thus acquires a contact surface of about 1 000 m2 and exercises a strong surface attraction to methanol, something like capillary action. During the night, although the compartment containing this activated carbon is not heated, the activated carbon attracts and adsorbs the molecules of methanol contained in the evaporator. The liquid methanol is evaporated, producing cold. The water around the evaporator turns to ice.
During the day, the active carbon saturated with methanol is reheated by the sun's rays. The force of adsorption diminishes in proportion as the heat increases, and the molecules of methanol are expelled by the pores of active carbon by desorption, as by boiling. The methanol condenses and runs into the evaporator. No chemical reaction is produced between the methanol and the carbon, adsorption being a physical, not chemical, phenomenon. Condenser and evaporator are joined by a tube, forming a tight assembly which keeps the surrounding air out and the methanol in so that its quantity does not change.
The system requires no moving parts and the cycles alternate in absolute silence. It is not necessary to change the position of the solar panel, which always points toward the sun at its zenith.
In a sunny climate, a solar collector with a surface of one square metre produces in 24 hours some 5 kg of ice, whose temperature is between -4 and -7 degrees centigrade. This ice is not even as cold as that which the ice compartment of an ordinary refrigerator can produce (-10 to -15°C), and a freezer can make even colder ice, but at least it allows food and, even more important, medicines and vaccines to be stored. According to WHO, these must be kept between 4 and 8 degrees. Gaspard prototypes, utilized in Senegal, French Polynesia, Guyana, and India have allowed the maintenance inside a compartment of 200 litres of a temperature of 4 degrees.
Despite its apparent simplicity, the system has demanded several years of research at the National Centre for Scientific Research (CNRS) in the laboratory of thermodynamics of fluids directed at Orsay (France) by Professor Francis Meunier. The CNRS patent has been developed by the engineers of Brissoneau and Lotz Marine (BLM), a subsidiary of Jeumont-Schneider.
Grd Paeye, service chief of research and development of the company, stresses that the apparent simplicity of Gaspard conceals a series of sophisticated and advanced techniques, notably for the manufacture of non-deteriorating compartments and vacuum assemblies, and the degassing to obtain the purest carbon possible, without gaseous residues which reduce the yield of the adsorption-desorption cycle.
Thermal shock permits nearly cylindrical carbon particles to be obtained from 2 to 3 micrometres (millionths of metres) long and 2 micrometres in diameter. On this cylinder, the pores form irregular orifices of 2.5 A diameter and a few in depth. These particles, with their numerous pores, constitute a "thermal sponge" which is saturated with methanol during the night.
The standard model manufactured till now looks like an isothermal box about a cubic metre in volume with a solar collector of about one square metre. The refrigeration compartment has a volume of 200 litres. The tests made in tropical countries have established that the adsorbent material is very stable and does not decompose and that the installation does not require either adjustment or maintenance. The refrigerator is guaranteed for ten years.
If the cold obtained is largely sufficient for keeping vaccines and small quantities of food, the ice is not cold enough to be commercially usable for preservation and transport of large quantities of meat and fish. The company envisages the manufacture of cold rooms of several dozen cubic metres with a view to adapting the same system for refrigerated transport vehicles and fishing boats. The gas exhaust of internal combustion engines could serve as a supplementary source of heat, which would make the transport of refrigeration machines or tons of ice to preserve shipped food unnecessary.