31 



CHAPTER II. 



THE SCIENCE OF FEEDING POULTRY. 



''rVHE scientific basis of a proper diet is 



I better understood now than formerly, and 



■*- its real principles may be explained in a 



way not only easy to understand, but to twr/c 



upon, which is the object in view. All who 



read at all now understand that life, 

 Purposes of from the physical standpoint, consists 

 I"*""!- of processes which involve constant 



change of substance and consump- 

 tion of material. That consumption must, of 

 course, be replaced ; and thus a certain amount of 

 food is necessary merely to keep or maintain the 

 body in its normal condition. Still more food 

 must be required if groivtii or increase of the 

 body has to be secured as well ; and yet further 

 food, if a.ny products of the organism are to be 

 maintained — such as milk, or eggs ; which, how- 

 ever, are a kind of growth. Yet further, it is 

 well known by experience that any special 

 activity, or work, involves more or less wear 

 and tear of the tissues, and so requires propor- 

 tionately more food ; and also that more is 

 required to maintain the ivarinth of the body 

 under unfavourable conditions. Greater supplies 

 of food than are necessary for these, so far as 

 they can be assimilated, are stored up in greater 

 bulk of muscle, and in fat ; which superabundant 

 tissues are the first to waste, or be consumed, 

 in an animal " starved " either by privation or 

 disease. 



Food, being thus required partly to make up 

 waste of tissue, partly to supply energy for 

 work, and partly to supply fuel for heat, must 

 contain in due proportion the elements of those 

 tissues, and those necessary for combustion. It 

 must also contain these in a form that can be 

 digested, since mere chemical composition is 

 not enough. An ox, for instance, can live on 

 grass, or the stalks of grain, and man cannot ; 

 but when the same elements have been elaborated 

 into the seeds of the grain (corn), these when 

 cooked form one of man's principal foods ; or 

 yet again, he can eat the ox itself. We know 

 broadly, however, what foods can be digested, 

 and are here concerned mainly with their com- 

 position, and that of the animal body whose 

 needs they are to supply. 



Taking such an animal body, by far the 

 larger portion of it consists of carbon, hydro- 

 gen, oxygen, and nitrogen ; in less 

 Composition quantity it contains sulphur, phos- 

 of the Body, phorus, and calcium (or lime: it is 

 well known that much of the bones 

 consists of lime phosphate) ; and still smaller 

 quantities of iron (chiefly in the blood) and of 

 salts containing chlorine, iodine, potassium, and 

 magnesium, with traces of other elements prob- 

 ably not essential. Of all these elements, 

 nitrogen is of the first importance, and is the 

 most distinguishing feature of animal or con- 

 scious life and activity. Itself a very inert 

 chemical element, it appears to group round 

 itself the various other elements, controlling 

 and organising their constant changes and 

 recombinations. In these offices it is consumed, 

 the more rapidly in proportion to the activity of 

 the animal. The carbon, hydrogen, and oxygen 

 are obviously chiefly employed in maintaining 

 energy and supporting combustion. 



Considering food and its disposal in the 

 body, we must not suppose that the nitrogen 

 is consumed entirely oi' chiefly in replenishing 

 direct waste of tissue. That is a popular error, 

 but a great error. Some of it does go to repair 

 actual waste of tissue ; but the larger part 

 appears to be consumed in carrying out those 

 constant changes which we call vital processes, 

 undergoing many and various chemical trans- 

 formations, but passing through the body in a 

 very short time in the performance of this func- 

 tion. Finally, the used nitrogen, both that wasted 

 from the tissues and that used up in the vital 

 processes, is e.xcreted mainly in the form of urea. 

 The far larger quantities of carbon and hydrogen 

 are used up — burnt up in a sense — in doing 

 work and producing warmth, using up oxygen 

 in the process. The used carbon is partly 

 excreted in the evacuations, but most of it in 

 breathing and perspiration. The hydrogen nearly 

 all passes off as water ; and since water is not 

 only taken in, but also formed in the body by 

 hydrogen combining with oxygen derived from 

 the food, more liquid is often excreted than is 

 drunk. Most of the salts and sulphur taken in 



