414 NUTRITION OF FARM ANIMALS 



In particular, however, the influence of those accessory sub- 

 stances or " growth substances " (498,499) which recent investi- 

 gations have shown to play such an important part in condition- 

 ing growth is to be considered. It seems not impossible tnat 

 high-protein feeds may in some such way have a stimulating 

 effect upon the capacity for growth quite independently of their 

 protein content. On the other hand, however, any such stimu- 

 lating effect upon growth would be absent in experiments made 

 with pure nutrients added to a basal ration of hay or straw, and 

 yet a fairly normal rate of increase seems to have been maintained. 

 On the whole, one can hardly fail of the impression that the 

 requirements for protein as such in growth have been over- 

 estimated and that the organism may utilize its protein supply 

 more economically than the current feeding standards would 

 indicate; in other words, that the actual protein supply may 

 be made considerably smaller than has been supposed before 

 it becomes a limiting factor in growth. Until this impression 

 is confirmed by more extensive investigation, however, it ap- 

 pears the safer course to adhere provisionally to the accepted 

 standards, and the protein requirements for growth as estimated 

 in Table IV b of the Appendix are based upon those formulated 

 by Kellner. 



Ash requirements 



492. Growth involves storage of ash. The growing animal, 

 like the mature one, requires mineral ingredients for the pur- 

 poses enumerated in Chapter V (268-272), but in addition to 

 this the formation of new tissue and especially of the skeleton 

 involves the storage of ash ingredients which must be derived 

 from the feed. This is shown clearly by the data recorded in 

 i (458) regarding the composition of the increase, its ash 

 content, aside from one exceptional case, ranging from 1.42 per 

 cent to 6.18 per cent. 



493. Rate of storage in growth. Data regarding the rate 

 of storage of mineral elements in growth are not very numerous 

 and are largely confined to experiments on the two important 

 elements calcium and phosphorus. The principal investiga- 

 tions are those of Soxhlet, 1 Neumann, 2 Lehmann, 3 and Weiske 4 



1 i er Ber. Versuch-Station Wien, pp. 101-155. 2 Jour. Landw., 41 (1893), 343- 

 3 Landw. Vers. Stat., 1 (1859), 68. 4 Jour. Landw., 21 (1873), 139- 



