154 RESPIRATION. 



The extent of respiratory surface has a very marked influence on the quantity of 

 watery vapor exhaled. This fact is very well shown by a comparison of the exhalation 

 in the adult and in old age, when the extent of respiratory surface is much diminished- 

 Barral found the exhalation in an old man less than half that of the adult. It is evident 

 that the absolute quantity of vapor exhaled is increased when respiration is accelerated. 

 The quantity of water in the blood also exerts an important influence. Valentin found 

 that the pulmonary transpiration was more than doubled in a man immediately after 

 drinking a large quantity of water. 



The vapor in the expired air is derived from the entire surface which is traversed in 

 respiration, and not exclusively from the air-cells. The air which passes into the lungs 

 derives a certain amount of moisture from the mouth, nares, and trachea. The great vas- 

 cularity of the mucous membranes in these situations as well as of the air-cells, and the 

 great number of mucous glands which they contain, serve to keep the respiratory sur- 

 faces constantly moist. This is important, for only moist membranes allow the free 

 passage of gases, which is of course essential to the process of respiration. 



Exhalation of Ammonia, Organic Matter, etc. Ammonia has long been recognized 

 as an exhalation from the human body in health, from the skin as well as the lungs. Dr. 

 Richardson calls attention, in his essay on the " Coagulation of the Blood," to the obser- 

 vations of Mr. Reade, Dr. Reuling, Viale and Latini, and others, on this point. Reuling 

 has shown that the quantity of ammonia in the expired air is increased in certain diseases, 

 particularly in uraemia. Its characters in the expired air are frequently so marked, that 

 patients who are entirely unacquainted with the pathology of uremia sometimes recog- 

 nize an ammoniacal odor in their own breath. 



The pulmonary surface exhales a small quantity of organic matter. This has never 

 been collected in sufficient quantity to enable us to recognize in it any peculiar or dis- 

 tinctive properties, but its presence may be demonstrated by the fact that a sponge com- 

 pletely 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 distinctive 

 of organic substances. 



It is well known that certain substances which are only occasionally found in the 

 blood may be eliminated by the lungs. Certain odorous principles in the breath are 

 pretty constant in those who take liquors habitually in considerable quantity. The odor 

 of garlics, onions, turpentine, and many other principles which are taken into the stom- 

 ach, may be recognized in the expired air. 



The action of the lungs in the elimination of certain gases, which are poisonous in 

 very small quantities when they are absorbed in the lungs and carried to the general 

 system in the arterial blood, is very well shown by the experiments of Bernard. Sulphu- 

 retted hydrogen, 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, w r hile they present 

 an immense and rapidly absorbing surface for volatile poisonous substances, are capable 

 of relieving the system of some of these substances 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 is a pretty 

 constant respiratory phenomenon. From a large number of experiments on dogs, rabbits, 

 fowls, and birds, these observers came to the conclusion that, when animals are subjected 

 to their habitual regimen, they exhale a quantity of nitrogen equal in weight to from yfg- 

 to -^5- of the weight of oxygen consumed. In birds, during inanition, they sometimes 

 observed an absorption of nitrogen, but this was rarely seen in mammals. Boussingault, 



