of Edinburgh, Session 1879 - 80 . 
565 
watery solution of fair strength, is not difficult; nothing, indeed, can 
well be easier. There are a number of methods which we might 
employ, and which are exact and easy of application; such are 
those of Liebig, of Heintz, and Ragsky, of Bunsen, of Huefner, 
and of Davy, all of which may be applied for its estimation 
in urine. 
With the blood it is another questidn, for here this substance 
exists in very small quantities (3 pairts in 10,000), mixed with a 
mass of organic matter, from which it has first to be separated in a 
tolerably pure form before the quantity can be ascertained. This 
separatio'n from the blood is the difficult task to be overcome, the 
estimation of the quantity will then bd easy. 
The Subject is dne df great importance iii physiological 
chemistry, Us all will admit, for it is d key to dur knowledge of 
the metaifolisni of albumindus substances in the bo’dy, nearly all 
the nitrogefi which is excreted passing out in this fdfni: 
This importance hag been thoroughly appreciated by chemists, 
and marly nieti df note have turned their attention to this sub- 
ject. 
It was Sir Robert Christisdn who first gave the stinlulatus to 
modern inquiry, for he it was who found a large amount (much 
above the normal) of urea in the blood of patients suffering from 
Bright’s disease. 
His method did not pretend td great chemical accuracy, for he 
took only tile clear serum of the blood, from which he crystallised 
out the urea as a nitrate after concentration. 
This discovery ranks with the highest that chemists have made 
in their investigations of the healthy and diseased tissues, and few 
indeed have been the facts gleaned gradually, and with difficulty in 
later years. 
Physiologists have endeavdured* but in vain, to found an 
accurate analytical process for its determination in blood, in 
order to investigate the many changes which dccur in its amount 
during different physiological and pathological conditions. 
Lecanu, Marclland, Simoii, Millon, Pettenkofer, Joseph Picard, 
Gscheidlen, and Drechsel have all worked with this object in 
view. 
Indeed the chemistry of blood is beset with difficulties, as all 
