EXHALATION OF NITROGEN 131 



tory surfaces constantly moist. This is important, for only moist mem- 

 branes allow the free passage of gases, which is of course essential to 

 the process of respiration. 



Exhalation of Ammonia, Organic Matter, etc. A small quantity of 

 ammonia is exhaled by the lungs in health, and this is increased in cer- 

 tain diseases, particularly in uremia. Its characters in the expired air 

 are frequently so marked that patients, who presumably are unacquainted 

 with the pathology of uremia, sometimes recognize an ammoniacal odor 

 in their own breath. 



The pulmonary surface exhales a small quantity of organic matter. 

 This has not been collected in sufficient quantity for analysis, but its 

 presence may be demonstrated by the fact that a sponge saturated with 

 the exhalations from the lungs, or the vapor from the lungs condensed 

 in a glass vessel, will undergo putrefaction, which is a property distinc- 

 tive of organic substances. 



It is well known that certain substances which are but occasionally 

 found in the blood may be eliminated by the lungs. Certain odorous 

 matters in the breath are constant in those who take liquors habitually 

 in considerable quantity. The odor of garlics, onions, turpentine and 

 of many other articles taken into the stomach may be recognized in the 

 expired air. 



The lungs eliminate certain gases that are poisonous in small quan- 

 tities when absorbed in the lungs and carried to the general system in 

 the arterial blood. Hydrogen monosulphide, which produces death in a 

 bird when it exists in the atmosphere in the proportion of one to eight 

 hundred, may be taken in solution into the stomach with impunity and 

 even be injected into the venous system ; in both instances being elimi- 

 nated by the lungs with great promptness and rapidity. The lungs, 

 while they present an immense and rapidly absorbing surface for 

 volatile poisonous substances, are capable of relieving the system of some 

 of these by exhalation when they find their way into the veins. 



Exhalation of Nitrogen. The most accurate direct experiments, 

 particularly those of Regnault and Reiset, show that the exhalation of 

 a small quantity of nitrogen by the lungs is nearly constant. As the 

 result of a large number of experiments, these observers came to the con- 

 clusion that when animals are subjected to their habitual regimen, they 

 exhale a quantity of nitrogen equal in weight to T ^ or -^ of the 

 weight of oxygen consumed. In birds, during inanition, they sometimes 

 observed an absorption of nitrogen, but this was rarely seen in mam- 

 mals. Boussingault, estimating the nitrogen taken into the body and 

 comparing it with the entire quantity discharged, arrived at the same 

 results in experiments upon a cow. Barral, by the same method, con- 



