NUTRITION. 345 



more known deficiencies occur. Many studies of this charcater have been 

 reported within the past few years. Not a few of these, however, are of doubt- 

 ful value for the elucidation of the etiology of abnormalities in bone develop- 

 ment and tissue growth because of the undue number of variables which have 

 been introduced b}^ the somewhat miscellaneous character of the foods. Our 

 effort has been directed primarily to secure observations under as carefully 

 controlled conditions of feeding as the circumstances and limitations of our 

 present knowledge will permit. Therefore, in many cases instead of using 

 foods as they occur naturally we have made use of mixtures of isolated food 

 materials. The very large number of experiments already undertaken point 

 to the complexity of the problem of tissue growth, particularly as it is exempli- 

 fied in the bones. Various factors doubtless interplay in ways that have not 

 hitherto been appreciated or taken into account. For example, seemingly 

 slight differences in the diet may lead to quite unlike pictures of structural 

 abnormalities, which will require extended careful analysis before any more 

 comprehensive generalizations can be drawn. We propose to continue these 

 experiments for some time; they include a consideration of some of the 

 antirachitic substances. 



The studies on the failure of many animals to breed on rations consisting of 

 purified proteins, fat, carbohydrate, and salt mixtures, together with fats 

 bearing vitamine A and yeast as a source of vitamine B, upon which they have 

 grown splendidly, are being continued. Mr. K. E. Mason, working in Pro- 

 fessor Harrison's laboratorj'- at Yale University, has found changes in the 

 gonads of the male in many instances. These can be averted or altered by 

 certain additions to the diet. For the present, the foremost emphasis is being 

 placed upon the determination of precisely the type of structural alterations 

 that present themselves in the testes. Later, when these are more clearly 

 understood and the conditions which give rise to the defects and their repair 

 are better ascertained, it may be more profitable to direct further attention to 

 the possible nature of the essential dietary components, without which the 

 developmental conditions essential for reproduction do not seem to be prop- 

 erly established. 



The failures to breed thus far observed in the seemingly well-nourished 

 animals are apparently not due merely to a shortage of vitamine A or vitamine 

 B in the diet. At any rate on the so-called synthetic rations, neither cod-liver 

 oil nor yeasts, which respectivelj'' furnish liberal quantities of the vitamines 

 referred to, have sufficed to insure fertility. "Fresh" food, as it is provided in 

 green vegetables, fruits, etc., is by no means indispensable for this function. 

 We have prepared a simple mixture of dried materials (consisting of alfalfa- 

 meal, casein, meat scrap, "red dog" flour, and salt) which furnishes all the 

 dietary components essential for maintenance, growth, reproduction, and 

 lactation in rats. We hope that the attempts to devise a simple inexpensive 

 mixture of this sort, in which we have been engaged for some time, will not be 

 without value to those who use the rat as a laboratory animal. 



The physiological functions of the inorganic components of the diet have 

 not received the attention which the great importance of the subject demands. 



In earlier studies we have pointed out to what extent limitations with respect 

 to a single ion such as calcium, potassium, phosphorus, etc., may affect the 

 nutritive well-being as evidenced by changes in body- weight. The quanti- 

 tative aspects of the subject demand further consideration, particularly in the 



