GRASS AND THE NATIONAL FOOD SUPPLY 459 



In the case of man, half the protein should be first-class protein, i.e. it 

 should be derived from meat and milk. 



In the case of animals, some recent work at the Hannah Dairy Research 

 Institute indicates that the protein contained in grass is of greater value 

 than the protein obtained from the seeds of plants. 



We will now consider the source of our food supply — how it comes from 

 the plant, and the animal through the plant. 



The original source of all human and animal energy is solar radiation. 

 Although plants take up some of their food (water, nitrogen and minerals) 

 through their roots, part of it is derived from the carbon dioxide in the 

 air, which, under the influence of sunlight, is decomposed by the green 

 colouring matter in the leaves, the carbon being assimilated and the oxygen 

 returned to the air. The compounds produced, carbohydrates and pro- 

 teins, have the highest chemical energy in the life-cycle of the plant. The 

 building up of the leaf is a storing up of chemical energy, and all the other 

 processes involved in a plant's life, including ripening to form seed, and the 

 sprouting of the new seed to form another plant, are but stages in the 

 degradation of that energy. The energy of all parasites on the plant is also 

 derived from the energy in the leaf, and the whole activity of the animal 

 world comes from this source. In other words, the animal world is but an 

 incident in the decay of leaf matter. 



The leaf of a plant may contain 50 per cent, to 90 per cent, water, but the 

 dry matter consists largely of soluble carbohydrates and proteins, together 

 with minerals and vitamins. When the plant begins to ripen, the carbo- 

 hydrates change into cellulose, and protein moves from the leaf into the 

 flower and seed. 



In the case of cereals and grasses — and probably of most other plants — 

 there is little further synthesis after the plant starts to ripen. All the 

 feeding value is present in a crop of grass — say at the end of May — and 

 though we leave the grass until the latter end of June before we cut it for 

 hay, the feeding value of the crop does not increase during that time. (The 

 reason we do not cut it for hay at the end of May is that in this stage of 

 growth it is so difficult to get the grass killed by the sun, so that there would 

 be grave danger of the stack taking fire spontaneously, and in any case 

 there would be considerable losses due to fermentation in the stack.) 



It will be useful at this stage to consider what are the chief foods men 

 eat, and from whence they come. 



We obtain the best quality protein from meat, milk, cheese and fish. 

 In these foods, the protein which originally existed in the leaf of the plant 

 (or a plankton in the sea) has been selected during metabolism by the 

 animal for its own purpose — since man is similarly constituted to the animals, 

 this selection is useful to us^and we can call these first-class protein foods. 

 Fruit and grain of various kinds also contain protein, but in this case the 

 protein from the leaf has been selected by the plant which has taken to the 

 seed those proteins necessary for plant regeneration. From the point of 

 view of the animal, the plant is not a particularly good selector of proteins 

 and we class these as second-class proteins. 



Man also eats leaves to some extent, especially spinach, cabbage and 

 lettuce, and these leaves are quite high in protein. In this case there has 

 been no selection of the leaf proteins by animal or plant, and it is probable 

 that this leaf protein is intermediate in value to man between animal and 

 other vegetable protein. 



Man obtains starch equivalent to supply heat energy, in the form of bread, 

 cereals, butter, fat and fruit, as well as, to a lesser extent, in meat, milk, 

 cheese, etc. 



