328 CARNEGIE INSTITUTION OF WASHINGTON. 



inferior animals purchased from a dealer before we had established our 

 own breeding-colony. None of our rats which have been continuously 

 supplied with a diet containing sufficient fat-soluble vitamine has ever 

 developed calculi, so far as our autopsies have revealed. 



Such calcuU are usually assumed to arise from ammoniacal decompo- 

 sition of the urine, caused by infection. All of our experimental animals 

 which have not had an adequate supply of the fat-soluble vitamine have 

 ultimately failed and many have shown a susceptibility to a form of infec- 

 tious eye disease speedily cured by foods containing fat-soluble vitamine. 

 An etiological relationship between the rations deficient in this vita- 

 mine and the formation of phosphatic calculi is indicated, since in every 

 case of calculi the animal had existed for some time on such a diet. 



In our report for 1916 we fiirnished data respecting the effect of 

 stunting on the physiological fife of rats after growth was resumed. 

 Our completed records now show females which were stunted to the 

 ages of 396, 538, 380, and 190 days respectively, giving birth to fitters 

 of young at 32 months (2 young), 28 months (3 young), 25 months 

 (2 young) , and 25 months (5 young) . Since the sexual life of all these 

 rats had extended well beyond the greatest age (22 months) at which 

 the menopause has been reported to occur, it appears as if such a pre- 

 liminary stunting period would lengthen the total span of life, unless 

 this were shortened by disease or accident. Unfortunately direct 

 evidence in support of this view was not furnished by any of these 

 animals, for all died of lung disease, although at an age of over 2 years. 

 This is a longer fife than two-thirds of our stock rats have attained. 



The experiments with chickens referred to in our last report have 

 encouraged us to continue them, for if it should be possible to feed 

 these birds successfully under strictly controlled conditions the essen- 

 tial factors for their nutrition could be established and many questions 

 now in dispute settled. Furthermore, since birds excrete at least 20 

 per cent of their food nitrogen as ammonia, and the balance cliiefly as 

 uric acid, it is probable that then* nitrogenous requirements may be in 

 some respects different from those of mammals. The source of such 

 excreted ammonia has not been established, norits possible relation to the 

 amide nitrogen which proteins yield as ammonia when boiled with acids. 



We have accordingly undertaken a new series of experiments, using 

 chickens taken directly from the incubator. The results thus far 

 obtained indicate ultimate success, but have not yet reached a point 

 where it is safe to draw final conclusions. 



Last year we stated that it was expected that the results of ana- 

 phylaxis experiments (then being tried by Professor H. G. Wells with 

 preparations of milk proteins which we had made) would soon enable 

 us to give an account of our study of the proteins of milk. The out- 

 come of these experiments showed that more work was necessary before 

 our results could be put in final form. This work is now practically 

 completed and will be published soon. 



