UREA. 



343 



CO, 



C 2 H 4 N 2 2 



C 8 H 9 N 3 4 



C 8 H 7 N 3 2 

 NaO,C 5 HN 2 2 +HO 



KO,C 5 HN 2 2 

 NH 4 0,2C 5 HN 2 2 +HO 



four days to produce a fatal result. A fatal result, however, is cer- 

 tain to follow, at the end of a longer or shorter time, if any one of 

 these substances be compelled to remain in the body, and accumu- 

 late in the animal tissues and fluids. 



The principal excrementitious substances known to exist in the 

 human body are as follows : 



1. Carbonic acid . 



2. Urea 



3. Creatine .... 



4. Creatinine 



5. Urate of soda . 



6. Urate of potassa 



7. Urate of ammonia 



The physiological relations of carbonic acid have already been 

 studied, at sufficient length, in the preceding chapters. 



The remaining excrementitious substances may be examined 

 together with the more propriety, since they are all ingredients of 

 a single excretory fluid, viz., the urine. 



UREA. This is a neutral, crystallizable, nitrogenous substance, 

 very readily soluble in water, and easily decomposed by various 

 external influences. It occurs 

 in the urine in the proportion 

 of 30 parts per thousand; in 

 the blood, according to Picard, 1 

 in the proportion of 0.16 per 

 thousand. The blood, how- 

 ever, is the source from which 

 this substance is supplied to 

 the urine; and it exists, ac- 

 cordingly, in but small quan- 

 tity in the circulating fluid, for 

 the reason that it is constantly 

 drained off by the kidneys. 

 But if the kidneys be extir- 



, n ,, , . n UREA, prepared from urine, and crystallized by 



pated, Or the renal arteries tied, 8 i ow evaporation. (After Lehmann.) 



or the excretion of urine sus- 

 pended by inflammation or otherwise, the urea then accumulates in 

 the blood, and presents itself there in considerable quantity. It has 

 been found in the blood, under these circumstances, in the propor- 



Fig. Ill 



In Milne Edwards, Logons sur la Physiologie, &c., vol. i. p. 297. 



