226 MANUAL OF CATTLE-FEEDING. 



Wisliceniis and otliers regarding the force value of the 

 nutrients, since it does not place the source of muscular 

 power in the albuminoids alone but in the joint action of 

 these and of non-nitrogenous matters. 



It is possible that Kellner's results, if confirmed by 

 fmther investigation, may modify this hypothesis some- 

 what. They at least suggest that when, under the influ- 

 ence of protracted work, the reserve of '' contractile mate- 

 rial " runs low, the protein of the muscle may be used to 

 supply the deficiency. 



In any case, it must be remembered that this hypothe- 

 sis is only a provisional one. Much work remains to be 

 done before we can have a full understanding of this im- 

 portant sixbject, and the chief value of such an hypothcbis 

 as this is to co-ordinate and arrange our knowledge, and 

 serve as the basis for fuither research. 



§ 8. Internal Work. 



In the two previous sections we have been considering 

 one particular form of work, viz., muscular exertion. 



As pointed out at the beginning of this chapter, there 

 are other forms of work which, though less obvious, are 

 of equal or even greater importance, and we now turn our 

 attention to these, grouping them under the convenient, if 

 not strictly accurate, name of internal work. 



The internal work of the body may be of three princi- 

 pal kinds : muscular work of the internal organs, produc- 

 tion of heat, and of chemical chans:es. 



of many of the most important internal organs involves 

 considerable muscular action, e, g,^ in the heart, the respi- 

 ratory muscles, and the digestive apparatus. Of these, 



