THE VITAMINES IN THE ANIMAL KINGDOM 



111 



wishes to demonstrate the nutritive value of a certain diet to carry 

 out feeding experiments with the same material on the next genera- 

 tion. For such a purpose, the rat is naturally specially suited. 

 Thus, it is possible to study, in a short time, not only the effect of 

 the diet upon the parents, but also to extend the observations on the 

 procreative power, the number of living young, and the lactation of 

 the mother. Judging by our experience, we deem it inadvisable to 



FIG. 21. RAT CAGE (MACALLUM) 



6, water cup; 7, flask for urine collection; 8, bulb by means of which urine, 

 is separated from feces (urine flows on the outside of the bulb into the flask 

 and feces falls into beaker) ; 9, food cups of various sizes; 10, funnels of various 

 sizes adapted to the age of the animal, so that the food may not be scattered. 



buy rats for experimental purposes; it is far better to raise them in 

 the laboratory. In this way we have the advantage of knowing the 

 parentage of the animals to be used. When one obtains a litter, it is 

 sometimes difficult to differentiate between the male and female. 

 To obviate this, we can utilize a method described by Jackson (310). 

 It is likewise of importance to use a cage so arranged as to be able to 

 control accurately the amount of food given, especially since rats 



