The Partition of Non-protein Nitrogen in the Blood of Fresh Water Fish

The introduction of microchemical methods has made possible many biological investigations which were formerly precluded by the di5culty of obtaining sufficient amounts of material. This has been the case with studies on the blood and urine of fish. The only accurate quantitative chemical data are found in the recent papers of Dr. Denis’ on marine fish, where she reports results which indicate that the composition of the blood and urine is not only different from that of other animals but may even vary in different species of fish. It has therefore seemed desirable to extend the studies to fresh water varieties in order Do gain further insight into the processes of metabolism in these animals. The present study has included determinations of total non-protein nitrogen, urea, ammonia, amino nitrogen, creatine, and creatinine in the whole blood and in the plasma of several species of fresh water fish. The nitrogen partition and the distribution of materials between plasma and corpuscles displayed several unique relationships. The creatine content of the plasma was greater than that of the corpuscles. Urea was present in surprisingly small quantities in most of the bloods and was in greater concentration in the corpuscles than in the plasma. This unequal distribution is in distinct contrast with the uniform diffusion of the compound throughout mammalian tissues. We have found that the amino nitrogen constitutes the major portion of the non-protein nitrogen in whole blood and is the largest single component. in plasma. The quantities present are