GROWTH 



417 



In order to compare the figures thus obtained with the results 

 recorded in the previous paragraph for the retention during 

 short periods, it is necessary to eliminate the influence of vary- 

 ing weight by computing the results per 1000. The retention 

 of calcium and phosphorus as thus computed agrees very well 

 with that found in the balance experiments with the exception 

 of Forbes' high result for phosphorus with the pig. On the 

 other hand the computed retention of the alkalies is strikingly 

 less, a fact for which no obvious reason appears. 



TABLE 105. AVERAGE DAILY RETENTION PER 1000 LIVE WEIGHT 



On the whole it appears that our knowledge of the ash require- 

 ments of growing animals, that is, of the actual amounts stored 

 up in normal growth, is quite fragmentary and unsatisfactory. 



495. Availability of ash ingredients of feed. If it is dif- 

 ficult to formulate from existing data any trustworthy estimates 

 of the ash requirements of growing animals, it is even more 

 difficult to make any definite statements regarding the total 

 amount of any particular element which must be supplied in 

 the feed in order to meet those requirements, although to the 

 extent to which the results recorded in the previous paragraphs 

 are trustworthy, it is possible to formulate the minimum supply. 

 Thus, Weiske's results on sheep show a retention of from 20 

 to 35 mgrs. of phosphorus per kilogram of live weight. If 

 these figures represent the normal requirements, it is evident 

 that a ration containing less than this amount would not supply 

 enough phosphorus for normal growth. What surplus above 

 this amount is necessary in the feed would depend on the pro- 

 portion of the feed phosphorus which is capable of solution in 



2 E 



