142 THE CHEMISTRY OP THE FARM 



During this experiemental diet the solid excrements 

 are collected and weighed, and are finally analysed by 

 the same chemical methods previously applied to the 

 food. Subject, therefore, to some small errors, arising 

 from intestinal secretions, we obtain by this plan the 

 amount of each constituent of the food which has 

 passed through the animal unabsorbed, and by differ- 

 ence the amount digested.^ 



(1) Experiments with Buminants. — Ruminating 

 animals possess an extensive digesting apparatus, con- 

 sisting of the so-called four stomachs, in addition to 

 the intestinal organs. Food takes a considerable time 

 in passing through this system. In changing the diet 

 of an ox, five days will generally elapse before the 

 remains of the preceding diet are entirely expelled by 

 the animal. Animals of this class are specially adapted 

 for the digestion of bulky foods containing much fibre. 



' The error introduced by reckoning intestinal secretions as un- 

 digested food is generally very small, but it becomes considerable in 

 certain cases. Thus, when an animal is fed on food very poor in 

 nitrogen, as straw, it sometimes appears as if no nitrogenous matter 

 had been digested, the nitrogen furnished by the intestinal secretions 

 being equal or greater than the nitrogen assimilated. We have, there- 

 fore, to bear in mind that the digestion coefficients found for nitro- 

 genous matter are always somewhat below the truth, and that this is 

 especially so in the case of foods poor in nitrogen. It is obvious, how- 

 ever, that even when the amount digested is incorrectly reckoned, the 

 net gain of nitrogenous matter to the animal is truly stated. As far as 

 the animal is concerned it comes to the same thing whether we say 

 that 70 per cent, of the nitrogenous matter in the food is assimilated, 

 while at the same time a quantity equal to 5 per cent, is excreted ; or 

 whether we say that 65 per cent, is assimilated, and take no note of 

 the excretion. The remarks just made apply equally to the digestion 

 coefficients found for fat, when this is present in very small quantity 

 (as in the case of hay or straw), biliary matters soluble in ether being 

 reckoned as undigested fat. 



