NUTRITION. 369 



shown that soon after the diet is changed from the ordinary mixed food 

 to the special diet containing starch, lard, protein-free milk, and a pure 

 protein, the intestinal flora becomes so simplified that fewer types of 

 bacteria are present. An increase in the number of gram-positive 

 organisms is frequently observed. No appreciable differences in the 

 bacterial flora have been observed after feeding various individual pure 

 proteins with the exception of zein. Two organisms related to the 

 acidophilous group of bacteria, which are found in the feces of the 

 stockroom rats in relatively large numbers, are frequently present in 

 the feces of the experimental rats to the exclusion of all other types, 

 except Bacillus hifidus of Tissier and Bacillus coli. B. hifidus is much 

 more abundant during the experimental feeding than wdth mixed food. 

 On the former the number of B. coli is greatly reduced. No definite 

 relationship was established between the bodily conditions (growth, 

 vigor, etc.) and the intestinal flora of the rats receiving the special diets. 

 The absence of indigestible material from our dietaries has fur- 

 nished an exceptional opportunity for studying the composition of the 

 feces resulting after the ingestion of pure nutrients. The experiments 

 demonstrate that a very considerable part of the fecal matter is made 

 up of bacterial cells and that, with exception of zein, the proteins are 

 very completely utilized. 



The preparation of large quantities of the milk proteins, "protein-free 

 milk," and butter-fat has led to the detection of the presence of sev- 

 eral hitherto unnoticed constituents of milk which demand extended 

 study. 



To insure against the loss of our now valuable breeding-colony of 

 white rats (by infection, fire, or other disaster) a branch colony has 

 been established in the laboratories of the Sheffield Scientific School. 

 These colonies are furnishing data regarding the average span of life 

 of rats kept under the laboratory conditions with which we are dealing, 

 so that suitable criteria as to what may be expected of any prolonged 

 dietary program shall be established. Incidentally our experience has 

 shown what can be accomplished by hygienic methods in the breeding 

 of experimental animals. It has been gratifying to be able to cooperate 

 with investigators in various parts of the country in furnishing experi- 

 mental animals and, to a limited extent, special feeding products. 



The study of the anaphylaxis reaction produced by carefully purified 

 preparations of vegetable proteins has been continued in cooperation 

 with Professor H. G. Wells and Mr. G. C. Lake and has been extended 

 to the complement-fixation reaction, the formation of precipitins, and 

 the production of passive anaphylaxis. 



It was found that the antisera produced by a brief immunization gave 

 the complement-fixation reaction only with the homologous protein. 

 By more prolonged immunization the reaction took place with heter- 

 ologous proteins of similar chemical and physical properties. At about 



