Digestion, Respiration and Calorimetry. 31 



striking variations from the normal. The range of digestibility 

 due to species, breed, age and live weight does not, under ordi- 

 nary conditions, vary more than from 2 to 4 per cent. 



51. Coarse and concentrated feeds combined. — When there is 

 added to a supply of coarse fodder, substances rich in piotein, 

 such as oil cake, oats, etc., the digestibility of the coarse fodder 

 is not thereby increased. The addition of a large quantity of 

 carbohydrates, such as sugar and starch, to a ration of coarse 

 forage, may reduce the digestibility of the protein and crude 

 fiber of the forage. The depression in digestibility caused by 

 the addition of the ca,rbohydrates is not apparent until the added 

 starch or sugar exceeds 10 per cent, of the dry matter of the 

 coarse forage, but is marked by the time the addition reaches 30 

 per cent. For example, at Weeude, when sheep were fed 1.75 

 pounds of hay and 8 ounces of starch per head daily, the diges- 

 tibility of the protein was reduced from 54 to 32 per cent. The 

 depression is reduced or suspended by the addition of a highly 

 nitrogenous feeding stuff, such as oil cake. The addition of fiat 

 to a ration does not increase the digestibility of the other constit- 

 uents. Salt does not affect digestion, though it may increase 

 consumption of feed and improve nutrition. 



The student should not confound the digestibility of feeding 

 stuffs with their final nutritive effect. While two animals may 

 each digest the same amount of nutrients from the same weight 

 of a given feed, one may give far better returns for the substances 

 taken into the body than the other. The utilization of the 

 nutrients of feeding materials is determined by the breed, indi- 

 viduality, condition of the animal, etc. 



52. Artificial digestion. — While vigorously prosecuting diges- 

 tion investigations with animals, the chemist has not been idle in 

 his efforts to find an easier and more rapid method of reaching 

 the same end. Stutzer has proposed a simple method for deter- 

 mining the digestibility of protein, by treating the substance 

 under investigation with weak solutions of pepsin and afterwards 

 of pancreatic fluid, care being taken to maintain the digesting 

 mass at the normal temperatuie of the animal body. The fluids 

 named act only on the protein of the food, hence this method 



