FEEDING OF ANIMALS. 309 



is frequently a considerable quantity as nitrates, the more the 

 less ripe the roots ; and we have sometimes found the amount 

 to be more than 10 per cent of the total nitrogen of the 

 roots. 



It is clear, therefore, that even supposing as little as 50 per Percentage 

 cent of the nitrogen of the roots to be available for, and cap- f^ 1 ™^ 

 able of, fat-formation, as assumed in the top line of the lower available 

 division of the table, that amount would generally include ^ a {f^ or ~ 

 other than albuminoid compounds. Nevertheless, Wolff in 

 his tables assumes the whole of the nitrogen of roots to be 

 digestible and available for the purposes of the system, since 

 it has been shown that amides are transformed in the body 

 and yield urea ; leaving, therefore, by-products of transfor- 

 mation available for expenditure in respiration, and so pro- 

 tecting the true albuminoids, or the carbohydrates. 



There is, however, so far as we are aware, no direct experi- Amides 

 mental evidence yet at command, indicating that the by- %^^ K 

 products of the transformation of amides may directly con- 

 tribute to the formation of fat. Eesults of independent ex- 

 perimenters have, however, shown that the heat of combus- 

 tion of asparagine for example, is only about, or little more 

 than, half that of albumin ; and supposing that the amides do 

 directly contribute to the formation of fat, it may safely be 

 concluded that a given quantity of amide would yield very 

 much less fat than an equal quantity of albuminoid. As 

 bearing upon this point, it is to be borne in mind that, on 

 the average, the amide bodies most frequently occurring in 

 food-stuffs have a higher percentage of nitrogen than the 

 albuminoids. Wolff estimates that whilst the nitrogen of food Wolff's 

 should be x 6.25 to represent albuminoids, 5.5 would, on cstimate - 

 the average, be a more appropriate factor for calculating the 

 amount of amide from that of the nitrogen. Further, he 

 admits that so far as the nitrogen in potatoes, roots, and 

 other food-stuffs exists as amides, the nutritive value of the 

 food is reduced ; nevertheless, as has been said, in his tables 

 he assumes the whole of the nitrogenous substance of roots 

 to be digestible, and of equal value with the albuminoids. 



Then, again, as generally more or less of the nitrogen in Nitrates 

 roots will exist as nitrates, it will so far not only have no °^ b iue°° d 

 food value, but it may be positively injurious. It may be 

 added that, other things being equal, the higher the percen- 

 tage of nitrogen in roots, the lower as a rule will be the pro- 

 portion of it as albuminoids, and the higher that as amides, 

 and as nitrates, &c. Further, in direct experiments at Eoth- 

 amsted with sheep feeding on roots alone, it was found that 

 whilst the animals even gained in weight on ripe roots, low unripe^ 

 in nitrogen, they actually lost on roots that were less ripe, roots. 



