MILK PRODUCTION 503 



That such is the case has long been taught, but many of the 

 early experiments upon which this teaching was based are 

 inconclusive in that they relate to the effect of adding protein- 

 rich feeding stuffs to relatively light rations low in protein. 1 

 The total digestible matter (energy supply) as well as the protein 

 in the rations was thus increased, sometimes by a considerable 

 amount, the quality of the protein sometimes improved, 

 and the proportions of the ash ingredients more or less altered, 

 while the possibility of the presence in the added feed of specific 

 stimulating substances (617-621) must be reckoned with. It is 

 illogical, therefore, to ascribe the beneficial effect entirely to 

 the increase in digestible protein, although this was doubtless 

 one of the factors. 



Jordan's investigations. Of more recent investigations in 

 which these sources of uncertainty were largely avoided those 

 of Jordan, some of the results of which as regards the utilization 

 of protein have already been cited (585), afford a good example 

 and may serve to illustrate the general method of such experi- 

 ments. Beginning with a ration fairly high in protein, the 

 proportion of this nutrient was gradually reduced to a com- 

 paratively low figure and then gradually increased again to the 

 original amount by an exchange in the rations between a nearly 

 pure protein (wheat gluten) and either maize or rice meal. 

 The total digestible matter was thus kept practically constant 

 while the probability of any specific effect was reduced to a 

 minimum. 



The actual yields of total milk solids and of milk protein in 

 the several periods are recorded in Table 139 and together 

 afford a fairly accurate measure of the amount of production. 

 Before drawing conclusions as to the influence of the varying 

 protein supply, however, it is necessary to take account of the 

 natural shrinkage in milk. Assuming that the rate of falling 

 off in milk due to advancing lactation, as shown by the differ- 

 ence between the first and last periods, was uniform (571), 

 the actual yields of solids and of protein as compared with 

 those which would have been anticipated had the feed re- 

 mained unchanged, were as follows : 



1 Compare Wolff's summary in Ernahrung der landw. Nutztiere, 1876, pp. 500- 

 550- 



