246 E. V. McCOLLUM 



the diet be carefully chosen in order that sufficient amounts of the "pro- 

 tective foods/' dairy products and leafy vegetables,' enter into the daily 

 menus to correct the deficiencies of the remainder of the diet. 



If we restrict a young rat for a time to a diet of cereal grains, legume 

 seeds and muscle meats, with or without tubers and other storage tissues, 

 of plants, it will fail to grow; will develop rickets, and at an early 

 age will die. As stated above, the nature of the deficiencies in this diet 

 are well understood to be lack of sufficient calcium, phosphorus, sodium, 

 chlorin and fat-soluble A. When sodium chlorid, calcium phosphate and 

 butter fat, or other fat having similar dietary properties (cod liver oil, egg 

 yolk, etc.) are added, the diet is made satisfactory and the animals develop 

 normally and go through successive generations without deterioration in 

 stamina. 



It is obvious that if the amount of protein in the diet is sufficiently low 

 to fail to supply the necessary material for the construction of new body 

 tissue, growth will be interfered with. A condition at least approximately 

 similar arises when the protein in the diet, though abundant, is of in- 

 ferior quality and therefore not effectively transformable into body pro- 

 teins. Both of these conditions may and do arise in human experience. 

 Under such a dietary regimen there is maintained a long lithe form, even 

 though growth may be suspended for a considerable period. No statistical 

 data have been collected to show whether rats in this condition, as the re- 

 sult of error in the protein factor as an uncomplicated fault, causes changes 

 in the form due to lengthening of the body and limbs, even when there 

 is no increase in body weight. If this is what happens, the changes de- 

 scribed would correspond in great measure to those described by Arou, 

 Waters, and Trowbridge as the result of underfeeding with a diet of such 

 a character as would induce growth and normal development provided 

 the amount of food available were sufficient. 



There are changes in form which are very characteristic when the diet 

 is faulty in certain other respects. This is especially true of diets de- 

 ficient in calcium. Even when the diet contains everything else that is 

 necessary for the normal development of a mammal, but the calcium con- 

 tent falls below the optimum, although not to an extent to interfere with 

 growth, the first generation of animals may look fairly normal, but will 

 age early. Their fertility will be low and infant mortality high, and the 

 few young which grow up will exhibit deformities which prevent their 

 reaching the full adult size. They are short and stocky, with deformities 

 especially of the ribs and spine. The displacement of the viscera down- 

 ward owing to the contraction of the thorax gives them a. pot-bellied ap- 

 pearance. The damage done by such a diet is permanent, for recovery 

 with expansion to the normal figure is not possible even when the faults in 

 the nutrition are corrected while the animals are still young chrono- 

 logically. 



