122 Progress of Foreign Science. 



The evaporated washings were subjected to alkohol, which dis- 

 solved the matter distinguished by the name of muco-extractive 

 substance, by Dr. Marcet, one of the first philosophers who charac- 

 terized it. M. Berzelius has since shewn, that this product might 

 be considered as a mixture of lactate of soda, and a peculiar animal 

 matter. Healthy blood having been exposed to perfectly similar 

 treatment, it was observed, that the blood of the animals operated 

 on afforded an alkoholic residuum twice more considerable. In 

 both cases, it was of a brown colour, soluble in water and alkohol, 

 strongly absorbent of moisture from the air, and precipitating the 

 acetate and nitrate of lead ; but that obtained from the blood of 

 the nephrotomized animals concreted into a white crystalline mass 

 with nitric acid. Water dissolved almost entirely the latter pro- 

 duct, and the aqueous solution saturated by means of a little car- 

 bonate of soda then evaporated, furnished a saline residuum from 

 which alkohol separated anew the animal matter, which appeared 

 with its primitive properties. These different characters, indicated 

 the presence of an animal matter susceptible of combination with 

 oxide of lead, as also of a considerable quantity of urea, and a 

 pretty large proportion of lactate of soda. When the combustible 

 ingredients were destroyed by the action of heat, the last substance 

 left much carbonate of soda. 



The urea was now purified, by converting the residuum of the 

 alkoholic treatment, into nitrate ; and this compound was left on 

 unsized paper for some hours. Thus the whole lactate of soda 

 was separated by its deliquescence, and sinking into the paper. 

 On re-dissolving the nitrate in water, there remained a small re- 

 siduum, which appears to be a combination of nitric acid with the 

 animal matter, precipitable by lead. The evaporation of the liquid 

 re-produced the nitrate of urea, in perfectly white pearly spangles. 

 It is easy by the known methods, to extract from them, the urea in 

 its pure crystalline state. By igneous analysis with oxide of cop- 

 per, MM. Prevost and Dumas ascertained the urea to be the same 

 as that obtained from urine. 



Important physiological corollaries may be deduced, from the 

 existence of urea in file blood, independently of the action of the 

 kidneys. This organ appears to be merely an eliminating surface, 

 analogous to the skin, as Dr. Rollo long ago supposed*. We are 

 still ignorant of the place where urea and the several ingredients 

 of the urine are formed. If any thing can throw light on this sub- 

 ject, it must, probably, be the examination of different urines in very 

 decided pathological cases. In fact, every chemist knows that 

 the urine of patients labouring under chronic hepatitis, contains 

 little or no urea ; which would seem to prove, that the functions of 

 the liver are necessary to its formation. 

 • The true seat of diabetes has been the subject of many learned 



* On Diabetes, p. 308. 



