'Dr John Davy on the Blood. 



23 



ammonia, and in its volatile state, does not exist in the 

 blood of other animals, and even in excessively minute 

 quantity, in the blood of birds. 



Keasoning from certain facts this seems probable. It is 

 known in the instance of man that the air expired com- 

 monly contains a minute quantity of this alkali, leading to 

 the inference that it is exhaled from the lungs, and previ- 

 ously existed in the blood. Dr Kichardson, in the work 

 already quoted, gives an account of many experiments 

 seemingly conclusive on this point. I may relate a few 

 which I liave made, employing the same method which he 

 used. The subjects of the trials were persons of different 

 ages, including infants, all in health. The expiration 

 directed on the moistened glass was made through one 

 nostril, the other and the mouth closed. Forty deep inspir- 

 ations in my own case were commonly sufficient to afford 

 distinct, though slight, traces of muriate of ammonia, as seen 

 with the high power after the evaporation of the acid, and 

 whilst the glass was still warm. Karely, in any instance, 

 have no traces of the salt been obtained. The indications, 

 however, have been variable, sometimes stronger, sometimes 

 feebler, as if depending on states of the system at different 

 times of the day and under different conditions, — a varia- 

 bility which Dr Kichardson also observed.* 



* In the experiments described above, the precaution was taken of breathing 

 through the nostril to avoid the risk of error which might occur were the 

 respiration through the mouth : in the latter case, the result might be vitiated, 

 and an erroneous inference made, were there a tooth undergoing decay, or a 

 bit of meat adhering, from which, if in a state of incipient putrefaction, 

 ammonia could not fail to be exhaled. When I have compared the breath 

 expired from the lungs througli the nostrils and through the mouth, I have 

 found stronger indications in most instances of ammonia from the latter than 

 from the former. I need hardly remark, it is so obvious to reason, that this 

 test of ammonia may have a useful applicatior. in medical practice — e.c/., in 

 diagnosing the earlier and later stages of pulmonary consumption. 



It may be worthy of mention, that the transparent limpid fluid which so 

 often drops from the nose in cold weather (as it were by distillation) has had, 

 as often as I have examined it, an alkaline reaction, and has afforded, after 

 the addition of hydrochloric acid, on evaporation, distinct crystals of muriate 

 of ammonia, mixed with which have been a few of common salt. The healthy 

 saliva, as is well known, has the same reaction, and, similarly treated, affords 

 crystals of the same kind as the preceding — tending to prove that ammonia 

 in each instance is eliminated, and is derived from the blood. 



