3^ 



THE BOOK OF POULTRY. 



of Food and 

 of the Body. 



food, after doing their work in the complex vital 

 processes, are excreted in the evacuations. 



These facts bring us to the point we are 

 directly and practically concerned with ; viz. 



the forms in which the above 

 Constituents elements exist, in the body to be 



fed and in the foods to be given it. 



Fortunately for us, both animals and 

 foods, upon analysis, are found to consist of 

 compounds which can be grouped into a small 

 number of classes, wWch fulfil the different 

 purposes above mentioned, and are found to- 

 gether in various degrees or proportions. These 

 are classed as follow : — 



1. The class containing nitrogen. These 

 were once termed proteids, but are now usually 

 called albuminoids ox albuminates, since albumen 

 (the white of an egg is nearly pure albumen 

 mixed with much water) is the chief type of 

 the class. There are certain vegetable principles 

 which also contain nitrogen, in the form of 

 ammonia (hence called amides), which some 

 writers consider less nutritive, and class by 

 themselves ; but there is no general agreement 

 upon this point, and we shall therefore follow 

 most authorities in classing all nitrogenous com- 

 pounds with the albuminoids. Fibrin in animals, 

 gluten in grain, casein in milk, legumin in peas, 

 belong to this group, almost any of which may 

 more or less replace another,* and serve, if 

 sufficient in proportion, as nitrogenous food. 

 That is the great principle to bear in mind. 



2. The next class consists of fats and oils, 

 often called hydro-carbons, and specially rich 

 in carbon. A certain portion of fat is necessary 

 to the healthy body itself ; so necessary, that 

 unless sufficient be supplied, a certain portion 

 even of the albuminoids will be decomposed in 

 order to form fat. Hence, fat in due proportion 

 is necessary to save or prevent such a wasteful 

 use of albuminoids. Besides this, we readily see 

 that this class finds its chief work in supplying 

 fuel for heat and energy. 



3. The next class, called carbo-hydrates, 

 consists of carbon in less proportion than in 

 fat, with hydrogen and oxygen in the propor- 

 tions of water. Starch, sugar, and gum are 

 leading compounds of this class in the vegetable 

 world. This group has plainly more or less in 

 common with the fats, and also supplies fuel for 

 heat and energy ; but it differs in not being 

 directly represented, as the fat group is, in the 

 animal body itself. Carbo-hydrates are, how- 

 ever, capable of being decomposed, and so 

 forming fat in the body. Thus they also save 

 waste of albuminoid foods ; in other words, a 



* It is not always fully the case, as is explained later on. 



due proportion of the carbon groups, as well 

 as of the albuminous compounds, is necessary 

 even for the increase of muscle or lean meat. 



4. One component of vegetable foods espe- 

 cially requires separate mention. Cellulose, 

 the material of which tough cell-walls and 

 woody fibre are composed, is of nearly the 

 same chemical composition as starch. Paper 

 and cotton-wool are examples of cellulose. But 

 this and kindred material exists in a form much 

 more indigestible by most animals, and entirely 

 so by some ; hence, for our purposes, we take 

 the harder of such constituents out of the carbo- 

 hydrates, into a separate class distinguished as 

 /lusk or fibre. A certain portion may be of 

 value, as a mechanical stimulus to the intestines; 

 but except for ruminant animals and birds, 

 which digest part of them, they are of little 

 value as food. 



5. The last class is that of salts and minerals. 

 Phosphorus and lime are needed for the bones; 

 sulphur for the feathers, besides a little for the 

 muscles ; salt for the whole range of digestive 

 processes ; alkaline salts to alkalinate the 

 blood, etc. 



Besides the above, there is in all foods a 

 very variable amount of hydrogen and o.xygen 

 in the proportions which form ivater, and may 

 be classed as such, though the water — as in the 

 case of apparently quite dry wheat or flour — 

 assumes in some way a solid form, and may not 

 be water at all. 



It is on the basis of these classes of com- 

 pounds that foods are analysed ; and the great 

 problem to be solved in feeding, or 

 Analysis and jn a dietary, is of the very simplest 



Nutritive 1 • j r i.i t.. • 



Ratio. kmd, SO far as theory goes. It is, 



to get a proper proportion betiveen 

 the albuminoids and the heat-producing groups 

 of fats and carbo-hydrates. A dietary so 

 arranged is called a properly " balanced " 

 dietary ; and if we give such a dietary, in 

 proper quantity and in digestible forms, the 

 animal will be properly fed. The actual pro- 

 portion in any food, or any dietary, is called 

 its " nutritive ratio." Thus a mixture of meals 

 whose nutritive ratio is 1:6, means that the 

 albuminoids in it are as one part by weight to 

 si.x parts of fats and carbo-hydrates. But in 

 calculating this ratio, one important modification 

 always has to be made. Fats are much more 

 fattening than starch or other carbo-hydrates, and 

 are more efficient generally, because (as already 

 noted) they are more rich in carbon. In adding 

 up the two groups, therefore, we must multiply 

 the figure for fats and oils by some figure ; then 

 we may add the product to the carbo-hydrates, 

 and reckon the total as one, for the nutritive ratio. 



