The Determination of the Urea in Chicken Blood

The observation was made some 6 years ago that chickens were not poisoned by the parenteral injection of large quantities of crystalline urease, unless urea was also injected (1). However, rabbits were killed after urease was injected when the blood ammonia nitrogen reached a value of 5 mg. per 100 cc. (2). These observations offer sufficient evidence to make many of the values reported for urea nitrogen in chicken blood, shown in Table I, questionable. Analyses of chicken blood, when the urea is hydrolyzed with crystalline urease, showed that the value for urea nitrogen was much lower than had been reported. According to Table I, there has been a gradual decrease in t,he values recorded for urea nitrogen in normal chicken blood during recent years until the average value of 0.7 mg. per 100 cc. of blood, as reported in Table II, is almost reached. The largest quantity of urea nitrogen found in the blood of forty-five normal chickens was 2.1 mg. per 100 cc. and the lowest 0.0 mg. Since the values obtained for the urea nitrogen content of normal chicken blood are extremely low, errors in methods for the determination of blood urea can be detected by the use of chicken blood. While the use of chicken blood will not disclose errors of less than 2 mg. of urea nitrogen per 100 cc. with any given method, it will enable the investigator to avoid many of the larger errors which have appeared in publications. The correct determination of the quantity of urea nitrogen in the blood of normal chickens is of value in the study of changes caused by disease. It has been reported that there is no change in the values for blood urea nitrogen of chickens with Rous sar-