S04 CARNEGIE INSTITUTION OF WASHINGTON. 



they failed to grow on diets which previous experience had shown to 

 be adequate for growth. An examination of our records showed that 

 a similar condition prevailed during the two preceding summers ; but 

 as we then had only a few young rats under observation our attention 

 was not especially attracted thereto. The same trouble has also 

 developed this summer. This condition is attended with diarrhea 

 and afflicts the rats on the natural as well as those on the artificial 

 "protein-free milk" foods. In order to determine whether or not 

 this intestinal disturbance was of bacterial origin, we have secured 

 the cooperation of Professor L. F. Rettger, of Yale University, who has 

 made a study of the intestinal flora of the rats in health, when afflicted 

 with this disease, and under a great variety of conditions of feeding. 

 Although Professor Rettger has not yet detected a definite cause for 

 the disease in question, he has obtained many interesting data 

 respecting the influence of our experimental diets on the intestinal 

 flora of the rat. He expects to be able to make a report on the results 

 of this work at an early date. 



Last year Dr. Ruth Wheeler undertook to repeat some of our earlier 

 experiences on the maintenance and growth of rats by feeding another 

 species — -albino mice — in comparable ways. A brief review of her 

 findings is published (see Bibliography, p. 54) . In many respects they 

 confirm our conclusions from the experiments with rats. Mice were 

 kept for very long periods (up to 6 months) on diets of isolated 

 food-stuffs containing a single protein. The comparative adequacy or 

 inadequacy of different proteins for maintenance, which we observed 

 with rats, was likewise found to be true in general for these smaller 

 animals. Stunting experiments were also conducted with them; and 

 it was found that the capacity to grow was still retained long after 

 the age at which the growth of mice normally ceases. In respect to 

 the dietary conditions appropriate for growth, however, the trials 

 on mice indicated that the suitable proportions of the nutrients — 

 particularly of protein and inorganic salts — may be quite different in 

 the smaller species from what pertains in larger ones. The experi- 

 ence gained from this work with the mice convinced us, further, that 

 our earlier selection of the rat as an experimental animal was well 

 advised. 



Besides the work here reported an extensive series of anaphylaxis 

 experiments have been conducted in cooperation with Professor H. G. 

 Wells, of the University of Chicago, the results of which have just 

 been published (c/. Bibliography, p. 54). This study has shown that 

 a common anaphylaxis reaction can be developed by two chemically 

 distinct but similar proteins of different biological origin, thus indi- 

 cating that the specificity of this reaction is determined by the chemi- 

 cal constitution of the protein rather than by its biological origin. 

 This is in harmony with the fact that chemically closely related pro- 



