2 4 6 



SCIENCE PROGRESS 



vitamine present in the fatty portion of fresh milk restores the 

 growing power to young rats and enables them to attain to their 

 normal size and weight. These animals were fed on the pre- 

 viously mentioned artificial food, and when they showed signs 

 of declining preparatory to death, butter was added to the diet. 

 Very shortly afterwards the decline was arrested, and growth 

 commenced once more. 



An interesting illustration of the fact that the activating 

 substance for growth is specific is afforded by one of Osborne 

 and Mendel's experiments where a rat became pregnant whilst 

 on the protein plus protein-free milk diet, and in due season 



no 



120 



60 



fco 



40 



Do^s 20 



40 



80 



100 



120 



160 



1 60 



200 



220 



Fig. 17. 

 (From the Journal of Biological Chemistry, vol. xii. 1912.) 



brought forth four young rats. The young rats were suckled 

 by the mother for 30 days, and during this time they seemed 

 to grow about as rapidly as the young of normal parents. 

 About this time, as a rule, young rats are wont to begin to 

 depend upon extraneous food for nourishment, and so three of 

 them were removed and fed separately. One of them received 

 a diet containing all the ingredients of milk. Note the normal 

 growth as represented in fig. 15. The other two rats were fed 

 on protein plus protein-free milk. Their curves (figs. 16 and 17) 

 reveal an attempt at growth, followed by collapse and death. 



