any value to an animal, must be rendered soluble, so that it can 

 be absorbed and carried through the system iii the blood. This 

 process of making the constituents of the food soluble is known 

 as digestion^ and is effected by the juices of the mouth, stomach, 

 intestines, etc. If animals could digest the whole of the albu- 

 menoids, or other parts of corn meal or shorts, then the analyses 

 above given would show the nutritive value. But it has been 

 found that such is not the case. ' Only a part of each substance 

 is digested. We may illustrate this point by supposing that 

 some one puts on the market a mixture of coal and gravel stones, 

 eighty pounds of the former and twenty pounds of the latter, in 

 each one hundred pounds. The value of this, as fuel, is only 

 that of the eighty pounds of coal, and any estimate based upon 

 the total weight would be erroneous. In the same way each con. 

 stituent of corn meal is made up of two parts, one digestible, cor- 

 responding to the coal in our assumed mixture ; the other, indi- 

 gestible, and corresponding to the gravel .stones. The value of 

 any kind of food is based, not on its total total composition, but 

 on the digestible parts. It is necessary, therefore, to know what 

 portion of each constituent is rendered available by the digest- 

 ive juices. The method employed is briefly as follows : An an- 

 imal is placed in a stall where no food can be wasted, a record of 

 all food con.sumed is kept, and from the analysis it is possible to 

 compute the exact amount of albuminoids, fibre, nitrogen free extract 

 zxx^fat, that has been taken into the system during the entire 

 experiment. All the parts of the food that are not digested pass 

 unchanged through the intestines and are found in the manure, 

 consequently, if all the manure is weighed and samples are an- 

 alysed, it is easy to compute the albumenoids, fibre, nitrogen, 

 free extract and fat, that has passed through the animal un- 

 chansfed, and these subtracted from the amounts taken into the 

 system will show what portion has been rendered available by 

 digestion. The degree of digestibility is usually expressed by 

 stating the number of pounds that are digestable in one hundred 

 pounds of each constituents. For example, it has been found 

 that of each one hundred pounds of albumenoids fed in corn 

 meal eighty-five pounds are digested. This eighty-five repre- 

 sents the per cent of digestibility of albuminoids in corn meal, 

 and is called digestion co-efficient. Of the nitrogen free extract,, 

 ninety-four out of every one hundred pounds is digestible, in 



9 



