CHAP. v. DIGESTIBLE CONSTITUENTS OF FOOD. 991 



exist as amide ; in potatoes 40 per cent. ; in turnips 50 per cent. ; 

 while in mangel 68 per cent, of the nitrogen is in the form of amide 

 and nitrate, only 37 per cent, existing as albuminoids. In well-made 

 hay the proportion of non-albuminoid nitrogen is less than in young 

 grass or clover. In silage, on the other hand, the amount of non- 

 albuminoids is much increased. In sour silage one-third of the 

 albuminoids originally present in the grass or clover has generally 

 disappeared, the nitrogen of the altered albuminoids remaining in the 

 form of amides or ammonium salts. 



" To calculate an albuminoid ratio correctly the amides present have 

 to be ranked with the non- albuminoid constituents of the food ; we 

 have, therefore, to inquire what is the feeding value of the amides of food 

 as compared with starch ? This has been ascertained only in the case 

 of one of the amides asparagine and for the present we have no 

 other figure to employ. The relatives of equal weights of starch and 

 asparagine are 



Starch 1 '00, Asparagine *49. 



" One point further must always be borne in mind in calculating the 

 albuminoid ratio of a food ; this is that we have to deal exclusively 

 with the digestible constituents of the food. The necessity of this is 

 obvious, for it is the character of the food assimilated by the animal 

 that we desire to know. If a sheep receiving undecorticated cotton cake 

 digests only 16 per cent, of the fibre present, while it digests 74 per cent, 

 of the albuminoids, it is evident that to the sheep the cotton cake is a very 

 different material from what it appears by the chemist's analysis. The 

 determinations of the proportion of each constituent digested by an 

 animal we owe almost exclusively to German experimenters ; in using 

 their figures we have, however, to bear in mind that the numbers 

 showing the percentage of albuminoids digested are always calculated 

 from determinations of the total nitrogen in the food and excrement, 

 and consequently do not correctly represent the digestibility of the 

 albuminoids. The digestibility shown for the albuminoids of the food 

 is indeed always in excess of the truth in those cases in which amides 

 or nitrates were present, as these are easily soluble bodies, and pass 

 readily into the system without the aid of any digestive process. It is, 

 however, quite easy, if we know the percentage of amides and nitrates 

 in a food, and assume that they are entirely digested, to calculate from 

 the German figures the percentage of tiue albuminoids digested. 



" It has been necessaiy to go into these details because much confusion 

 has arisen about the albuminoid ratio : we will now turn to the practical 

 aspect of the subject. In the following table we give a few illustrations 

 of the ratio of albuminoids to non-albuminoids in some common foods, 

 assumed to be of average composition. In a second column is given 

 the ratio of nitrogenous to non-nitrogenous substance ; this latter ratio 

 will correspond nearly with those quoted by Wolff; but, as we have 

 already seen, such ratios cannot properly be called albuminoid 

 ratios. 



