24 



Dr John Davy on the Blocd. 



I have obtained also traces of the volatile alkali from 

 the breath of other animals. In the instances of the horse 

 and duck they were unmistakeable. The trials were made 

 in the same manner as that described — the mouth and one 

 nostril closed. The time occupied was about five minutes. 

 In the instance of the common fowl, no trace was detected ; 

 but as its nostril is very much smaller than that of the 

 duck, it is not so easy to direct the current of expired air 

 on the spot moistened with the acid. The crystals obtained 

 from the breath of the horse were so large as to be dis- 

 tinctly seen with a glass of a quarter-inch power, yet were 

 hardly appreciable by weight. These trials were made in 

 the open air. 



Besides an exhalation of ammonia from the lungs, it is 

 also well ascertained that it is excreted by the skin. It 

 has been found in sweat by Berzelius in the form of the 

 muriate, and has been detected by other inquirers. Like 

 Dr Richardson, I have found it evolved even in insensible 

 perspiration. Here is an instance : — When the thermometer 

 in my room was 70°, a slip of glass moistened with the 

 dilute acid was kept under the palm of the warm hand for 

 ten minutes, carefully avoiding contact ; now, on examina- 

 tion, after evaporation of the acid, a trace of muriate of 

 ammonia was obtained in minute crystals, sufficiently dis- 

 tinct, and more than. I could have expected. This experi- 

 ment I have repeated on myself and others with like result. 

 The warmer the weather, and the higher the temperature 

 of the surface, the larger commonly has been the proportion 

 of the salt formed. It is noteworthy, that when the glass, 

 without the addition of the acid, had been exposed to 

 the insensible perspiration during the same length of time, 

 no trace of salt was detected on it ; leading to the inference 

 that the ammonia exhaled is in the volatile form, and pro- 

 bably in union with carbonic acid. 



Reflecting on these facts, it seemed probable that if 

 ammonia in the volatile state exists in the blood, it is likely 

 to be in a larger proportion in venous than in arterial 

 blood, on the supposition that it is exhaled from the lungs 

 with carbonic acid in the act of expiration. To test this I 

 made trial of the two kinds of blood, one from the jugular 



