54 
UREA. 
with ; secondly, from agents taken in by respiratory action ; 
thirdly, from causes acting upon any external surface or 
tissue of the frame ; fourthly, from the arrest, or even from 
the impeded action of any eliminatory function ; fifthly, from 
the absorption of any morbid product into the circulating 
system ; sixthly, from the abnormal condition of the vital 
force, or of the nervous centres acting upon the heart and 
blood-vessels, having a reciprocating influence upon the 
haemato-globuline circulating in the blood. Copious illustra- 
tions were given on each of these heads. The effects of food, 
emanations from various sources of pollution, absorption of 
“ sanies,” and of any puriform secretion into the circulating 
channels, were fully discussed. Attention was directed to the 
evils caused by defects of the various excretory functions, 
the due performance of which was necessary to the healthy 
state of the blood; and lastly, to the agents, extrinsic or 
intrinsic, which either excite or lower the nervous system, 
and thus influence the vascular system. The author re- 
marked upon the operation of these agents upon the blood, 
manifested by a degeneration or waste of the red blood cor- 
puscles. The changes they caused were said to be the 
following : — 1st. A complete metamorphosis or change of the 
haemato-globuline. 2d. A portion of the red blood corpuscles 
being transmuted into bile. 3d. The change of epithelial 
cells from the kidneys and mucous follicles into red blood 
corpuscles. 4th. Their gradual expenditure in the elabora- 
tion of the genital secretions in both sexes. Reference was 
made to Mr. Simon’s nomenclature of blood diseases, and a 
review passed upon some of the most striking malignant 
diseases arising from an altered state of the blood. In con- 
clusion, some illustrative cases were given . — Read at the 
Royal Med . and Chirurg . Society . 
UREA. 
Urea is one of the most important immediate principles 
of urine, where it is known to exist in the free state, and, pro- 
bably, also combined with chloride of sodium. 
Urea was discovered, in 1771, by Rouelle, junior, who 
observed its presence in urine. Cruikshanks, in 1798, ob- 
tained it in the crystallised form. Fourcroy and Vauquelin 
gave it its present name. Its existence in the aqueous and 
vitreous humour of the eye was detected by Millon; and 
Wohler found it in the liquor amnii. Pettenkoffer traced it 
in the saliva; and, according to Stass, urea may be extracted 
