Dr J ohn Davy on the Blood, 



25 



vein, the other from the carotid artery of a lamb about to 

 be slaughtered. The weather at the time was warm, the 

 thermometer in the shade 75°. The quantity of blood col- 

 lected of each kind was about the same, the recipient vessels 

 of like size, capable of holding about three ounces. The 

 instant they were filled they were covered with a plate 

 of glass partially moistened with the acid. After fifteen 

 minutes an examination was made in the manner before 

 described. On the glass exposed to the arterial blood no 

 muriate of ammonia could be detected with the high power 

 of the microscope ; but on that exposed to the venous a 

 trace of the salt was observed. 



I shall now mention some other instances in which, 

 using the same method, I have examined the blood in spe- 

 cial quest of ammonia. The animals from which the blood 

 was obtained were the common fowl, the duck, horse, sheep, 

 heifer, calf, sea- trout (Salmo trutta), and toad. In all the 

 experiments, in those already described and those which 

 follow, due precautions were taken to avoid as much as pos- 

 sible error, and this both in relation to the acid used and 

 the place where the trials were made ; in many instances, 

 for greater security, a comparative experiment was made 

 under the same circumstances as to time and locality, with 

 the acid alone and the blood alone. The results of these 

 were negative.* 



1. Of the Common Fowl. — When the temperature of the 

 open air was 47°, a hen of about three years old was killed 

 by the division of the great cervical vessels. The blood that 

 first flowed was received into a wine-glass. It coagulated 

 almost instantly, certainly in less than half a minute. A 

 plate of glass moistened with acid was immediately placee 

 over it. After about five minutes it was taken off, and the 

 acid evaporated ; no trace of ammonia could be detected on 

 it, on inspecting it with the high power. The blood which 

 flowed last, which also rapidly coagulated, and was nearly 



* In my earlier experiments, those made in 1859, the test employed for 

 the detection of ammonia was a glass rod, moistened with hydrochloric acid 

 of reduced strength, which, as has been well pointed out by Dr Richardson, 

 is less delicate, less to be relied on than that of the crystalline formation of 

 muriate of ammonia, as seen with the microscope. 



NEW SERIES. VOL. XIX. NO. I. JANUARY 1864. D 



