1 74 SECONDAR V FEEDING STUFFS 



with a little spice. The detection and estimation of 

 such substances is attended with no difficulty. 



Digestibility of Feeding Stuffs. 



The measurement of the digestibility of the various constituents 

 of a feeding stuff is of prime importance, since the animal is only 

 able to utilise that portion of the food which is broken down in the 

 alimentary canal. Ordinary chemical analysis is unable to distin- 

 guish between the total food nutrients and those which are 

 digestible, and recourse is had (i) to digestibility trials with 

 animals, or (2) to methods of artificial digestion. In the former 

 method, the fasces of the animal are collected and weighed and the 

 constituents determined as in the food. The second method has 

 only been elaborated with any success in the case of the proteins, 

 which may be artificially digested by means of pepsin. 



174. Digestibility of Protein. 



A pepsin solution is prepared by dissolving i gram 

 of commercial pepsin, e.g. Witte's pepsin, in i litre of 

 0-33 per cent, hydrochloric acid. 



The food-stuff (wheat or oilcake will do well for 

 practice) is ground to a fine meal and 2 grams are 

 weighed out and suspended in a flask in 100 c.c. of the 

 pepsin solution. A drop or two of toluene is added to 

 keep the liquid aseptic, the flask is plugged with cotton 

 wool and maintained in a thermostat, with occasional 

 shaking, for twelve hours at 37-5° C. At the end of that 

 time the contents of the flask are poured on a wet filter, 

 the residue washed well with lukewarm water, and then 

 with alcohol and ether. Filter paper and contents are 

 then transferred to a Kjeldahl flask and the protein 

 estimated in the usual way. The total protein is 

 estimated in the food-stuff, and the amount which has 

 been digested is calculated per cent. 



