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CARNEGIE INSTITUTION OF WASHINGTON. 



As regards the creatinine, numerous analyses made on crawfish blood at 

 Tortugas firmly established the fact, already discovered in my earlier studies 

 of the invertebrate blood, that there is none present. Owing to the great 

 concentration of the filtrates, the equivalent of 8 c. c. blood was used for a 

 creatinine determination. The color developed with the picric-acid reagent 

 within 15 minutes can be matched almost perfectly against a blank, with 

 distilled water in place of the blood filtrate. If one allows a much longer 

 time to elapse, a certain amount of red color develops, which depends primarily 

 upon the sugar concentration of the particular sample, also on the time. Of 

 course, even pure sugar solutions will give this reaction, if enough time is 

 allowed, and it is possible that the quantitative results reported in the litera- 

 ture showing comparatively high creatinine values can be attributed to some 

 technical error. From the writer's own experience, both earlier, extending to 

 25 specimens of various arthropods, and the even more extensive recent experi- 

 ence with the Tortugas crawfish, it can be stated unequivocally that, at any 

 rate in these marine animals, there is no creatinine in the blood. 



The question of the relation existing between the nutritive state of the 

 animal and the composition of its blood was attacked also by direct experi- 

 ment. For this purpose the blood composition was compared before and at 

 various periods after the intramuscular injection of the following substances: 

 urea, ammonium sulphate, glucose, sucrose. In view of the shortness of the 

 available time, it seemed best to inject these substances in pairs, thus: urea 

 and glucose, ammonium sulphate and sucrose. The substance was dissolved 

 in sea-water and injected into the muscles of the thorax. The amount of 

 urea given varied from 0.4 to 1.0 gram, of ammonium sulphate 0.5 gram, of 

 glucose 0.4 to 0.8 gram, and of sucrose 0.4 to 0.5 gram. Briefly summarized, 

 the results were as follows : Ammonium sulphate is rapidly eliminated from 

 the body. Two hours after an injection it is not only completely gone, but 

 the non-protein content of the blood is also markedly diminished. Injections 

 of urea raise the non-protein N content of the blood in a very striking manner, 

 and it requires perhaps no less than 12 hours for the original nitrogen-level 

 to become reestablished. 



Although in some experiments it was found that nearly all, or at any rate 

 a very large proportion, of the non-protein nitrogen in the blood 1 to 4 hours 

 after the injection is urea-nitrogen, as one might expect, this is not invariably 



