AGEICULTURAL CHEMISTRY 199 is not best adapted to sustain the labor of the horse. Where the animal's functions are re- quired to differ in their essential nature, there the food must also differ ; and we cannot carry the peculiar aptitude of an animal to the high- est pitch without particular attention to the quality of the food. In fact, by a careful se- lection of the food we can change the charac- ter of the animal ; and when at the same time other physiological circumstances, climate, &c., are suitably regulated, it is possible in the course of a few generations to impress new characters on a race. In this way the various breeds of cattle, swine, &c., have originated. A thorough understanding of the reciprocal relations between food and functional develop- ment is therefore of the highest consequence to the practical agriculturist. It cannot be pretended that science in its present state fur- nishes very extensive or satisfactory knowledge on these points. But physiological chemistry has developed some truths which warrant the hope of progress in this direction. The study of changes in the animal body has shown that there are two chief processes concerned in the maintenance of life, viz., nutrition and respira- tion. We use the word nutrition in a some- what qualified sense, understanding by it the support of the working parts of the animal the muscular, nervous, and cartilaginous tis- sues. These tissues contain nitrogen as an in- variable ingredient, and for their development nitrogenous food, or food containing albumen, caseine, and fibrine, is indispensable. No work can be done on food consisting exclusively of starch, sugar, and oil, because these bodies cannot supply the nitrogen which is required for the organization of the working tissues. In the normal growth of active animals, the non-nitrogenous principles of the food are con- sumed in the respiratory process. These bodies are brought into contact with the oxygen in- haled by the lungs, and are burned into car- bonic acid and water, which pass off in the expired breath. The heat of the animal is sustained by this combustion. In sluggish animals which ingest large quantities of non- nitrogenous food, the excess accumulates in their bodies in the form of fat. Great activity and full respiration are incompatible with this accumulation. The application of these facts is obvious. To keep a horse or an ox in work- ing condition, we give a food rich in nitrogen, as oats; to fatten an animal, we use a food richer in starch, sugar, and oil. Experiments have been made with a view to determine what should be the relation between the nitro- genous and non-nitrogenous elements of the food for working, fattening, and milk-giv- ing animals, as well as for otherwise deter- mining the statics of nutrition. In Saxony much attention has been devoted to these sub- jects, and experiments in feeding, conducted in that country, have shown that breeding and dairy cattle thrive best when each animal re- ceives daily for every 100 Ibs. of its live weight 2-5 to 2-8 Ibs. of food (calculated in the dry' state), which contains 0-25 to 0-30 Ib. of ni- trogenous or nutritive, and 1-25 to 1-40 Ib. of non-nitrogenous or respiratory, fat-forming material. The stomachs of cattle are adapted for a food containing a large quantity of woody fibre, which is mostly indigestible, and seems to perform a merely mechanical function in exciting the digestive apparatus. In the trials just alluded to, the best proportion of woody fibre was found to be one fifth of the whole dry matter. Years ago attempts were made to construct from chemical analyses tables of nu- tritive equivalents, for exhibiting the compar- ative value of different sorts of food. The first essays of this kind were very crude. Later results more nearly accord with experience, being founded on more complete analyses, and with a better knowledge of the wants of the animal; but there are many circumstances whose effect on the nourishing capacity of the different kinds of food has not yet been thor- oughly studied. It has been proved that the use of nitrogenous manures increases the rela- tive as well as absolute quantity of blood- forming substances in the grain. The digesti- bility and consequent nutritive effect of the grasses is greatest when they are cut just after attaining full flower, or, at any rate, before the seeds have hardened, as at this period they contain the maximum of soluble matters. Af- terward the quantity of woody fibre increases. The cereals yield more and better flour when cut while the berry is still in the milk, and for a similar reason. The use of cooked food for cattle depends upon the fact that the cooking of food by boiling or steaming is equivalent to the preliminary processes of digestion; as in both cases cellulose, starch, dextrine, and the gums are progressively converted into grape sugar. Toward the end of the last century the vague and ancient notions that air, water, oil, and salt formed the nutrition of plants, began to be modified with some truer ideas. In 1761 Wallerius, a Swede, in his treatise Fundamenta Agricultural Chemica, recognized to some extent the connection between the composition of the ash of plants and that of the soil. Bergman, the great Swedish chem- ist, Palissy, and Reaumur also sought to study the chemical conditions of vegetable growth. In 1802 Sir Humphry Davy was invited to lec- ture before the English board of agriculture, and thereafter made numerous important ob- servations. H recognized the fertilizing effects of ammonia, and analyzed numerous manures, including guano. About the same time Sen- nebier and De Saussure laid the" foundations of vegetable physiology, demonstrated the assimi- lation of carbonic acid and water from the air, and indicated atmospheric ammonia as the probable source of nitrogen to the plant. De Saussure also fully recognized the nature, importance, and source of the ingredients of the ash, and studied the life of the plant in all its phases. In 1832 Sprengel made numerous
