110 . THE VITAMINES 



scurvy while guinea pigs with their characteristic purine metabo- 

 lism occupy a middle position. Whether these conceptions may 

 still be regarded as correct is not certain, for in the first place, a 

 type of beriberi in dogs and rats has been described and secondly, 

 there is a possibility of another explanation of the above mentioned 

 observations. At all events, we wish to leave the question open for 

 further investigation, particularly since beriberi has not been defi- 

 nitely demonstrated in certain animals, and may even be confused 

 with other pathological conditions. The criteria for the recognition 

 of beriberi, such as the fatty degeneration of the nerves, are not 

 specific symptoms of beriberi. We have fed white rice for along 

 time to rats, rabbits and guinea pigs, without noticing any kind of a 

 symptom to suggest beriberi. The other explanation, of the differ- 

 ent behavior of certain animals on a diet of white rice, we find in 

 the unknown role of the bacterial intestinal flora, the significance of 

 which has already been mentioned (p. 76) in the chapter, "Life 

 Without Bacteria." We come now to the consideration of the impor- 

 tance of the vitamines for various mammals. 



Rats 



Rats have been extensively used as experimental animals in the 

 last 10 years in the attempt to solve the problems of nutrition, and 

 for vitamine research. The reason for this is that rats breed easily, 

 do not consume much food and are not particular in their taste. The 

 fact that a greater number of these animals may be used at one time 

 for an investigation makes the results much more certain. Since in 

 most problems of nutrition, the food must be specially prepared, as 

 a rule, the small amount ingested is of practical significance. Rats 

 live about 3 years and reach sexual maturity very early. The 

 pregnancy lasts 3 weeks and the offspring is numerous; the number 

 of young varies from 6 to 12 according to the age of the parents and 

 their nutritive condition. The young rats begin to eat of their own 

 accord after 3 to 4 weeks, and may be used for feeding experiments 

 when they weigh 30 grams, though it is better to wait till they 

 weigh from 40 to 60 grams. It has been shown by many investiga- 

 tors, among them McCollum, Simmonds and Pitz (309), that inade- 

 quacies of the diet are manifested in a diminished milk secretion of 

 the mother, or else in a poor state of health of the young, although 

 the parents show no such signs. It is therefore desirable, if one 



