NUTRITION 103 



this kind, an animal consumed 25 Ibs. of hay, and dropped, on 

 the average, 60 Ibs. of faeces daily during the time (about 

 three weeks) the experiment lasted. The composition of 

 these products was found, on analysis, to be as follows : 



Hay Faeces 



(per cent.). (per cent.). 



Moisture 14/2 84*0 



Ash 5-8 2-4 



Organic matter 8o - o 13-6 



lOO'O lOO'O 



The total quantities of organic matter consumed and 

 excreted were therefore 



80 x 25 13-6 x 60 



= 2o'o Ibs. = 8' 1 6 Ibs. 



100 100 



The digestibility of the organic matter was then calculated 

 thus 



100 (20*0 8*2) 



- = 59-0 per cent. 



This figure 59 per cent. is called the coefficient of 

 digestibility of the organic matter in that food. The co- 

 efficient of digestibility of the protein, fat, and other con- 

 stituents can be determined in a similar manner. The data 

 required in each case are the quantities of the particular 

 ingredient consumed and excreted. 



There are, of course, considerable practical difficulties 

 connected with experiments of this kind. Suitable arrange- 

 ments must be made for the collection, weighing, and sampling 

 of the faeces; and care must be exercised to prevent it 

 becoming mixed with urine, litter, or other extraneous matter. 



Owing to the difference in the capacity of the stomach and 

 intestines, the time required for the undigested portion of the 

 food to pass out of the body varies considerably in different 

 types of animals. For ruminants, it is estimated at three or 

 four days, for pigs thirty to forty hours, and for horses about 

 twenty-four hours. The only way, therefore, to ensure proper 

 correspondence between the food consumed and the faeces 

 excreted is to extend the time of the experiment. 



