238 



SCIENCE PROGRESS 



America, and various other workers in Germany and elsewhere, 

 have shown that although an artificial diet may be constructed 

 which will maintain full-grown rats in health for a few weeks, 

 yet, after this time, they invariably begin to decline and slowly 

 die. What is even more remarkable is that it is impossible in 

 the case of young rats for normal growth to take place when 

 only an artificial diet is supplied, but that the addition of small 



itQ Days. 



Fig. 9. 



White circles : — Rats on artificial diet alone. 



Black circles :— Rats on artificial diet + 2 c.c. milk per rat per diem. 



(From the Journal of Physiology, vol. xliv. 1912.) 



traces of other substances, such as fresh milk, is quite sufficient 

 to transform the inadequate into a most nourishing diet. 



Hopkins's experiments were carried out on young rats about 

 35 to 50 grammes in weight, e.g. of such a size as would normally 

 double itself in about twenty days. The rats were kept in cages, 

 two in a cage, and were weighed every three or four days. The 

 artificial diet consisted ot casein, starch, cane sugar, lard, and 

 salts, mixed up with a little water into a stiff dough ; and the 

 amount of food daily eaten was accurately estimated, the average 



