CONDITIONS INFLUENCING DIGESTION 135 



Chester White pigs would digest rations differently from 

 Jerseys, Merinoes, and Yorkshires. 



Young animals seem to digest high-quality coarse 

 foods. and grains as eflBciently as older ones of the same 

 species, which is probably contrary to the popular belief. 

 There is doubtless a variation in the digestive power of 

 individual animals, but the data so far collected do not 

 show this with any degree of definiteness. In those in- 

 stances where the same four or more steers or sheep have 

 been used in determining the digestibility of several 

 feeding-stuffs, the highest coefficients were obtained 

 sometimes with one animal and sometimes with another. 



197. Determination of digestibility. — If we accept 

 as the undigested food the dry matter of the solid excre- 

 ment, which is practically in accordance with the fact, we 

 have only to subtract the dry fecal residue from the dry 

 matter of the ingested food in order to ascertain the 

 amount and proportion digested. All digestion experi- 

 ments have proceeded on this basis. Animals have been 

 fed at regular intervals a uniform quantity of carefully 

 analyzed food and the feces have been collected, weighed, 

 and analyzed. From the data thus obtained, the digestion 

 coefficients have been calculated. The ioaethod and the 

 mathematics of such experiments are so simple that cor- 

 rect results seem very easy to obtain and they do possess 

 an accuracy sufficiently approximate to truth to render 

 them useful in practice. As digestion trials are usually 

 conducted, the coefficients of digestibility obtained for 

 the dry matter and total organic matter represent, we 

 have reason to believe, very nearly the actual digestible 

 matter in the particular material studied. The propor- 

 tions secured for particular classes of nutrients may be 

 less accurate, for reasons that will appear. We cannot 



