Chap, xvi.] PHYSIOLOGICAL OFFICE OF EESPIEATIOII. 245 



sometimes there is an excess, sometimes a deficit. Thus, there 

 is a retention of azote in the organism during inanition, and even 

 several days after its cessation. It is the same when the animal 

 under observation is suSering, perhaps because then it submits 

 itself spontaneously to a relative inanition. 



The pulmonary membrane, offering to contact with the air a 

 large surface at a tolerably high temperature, is naturally the 

 seat of transpiration, of an abundant aqueous evaporation. 

 Lavoisier and Seguin, whom we must always quote when respira- 

 tion is in question, have estimated at 7"90 grammes in an hour, 

 or about 569 grammes, the quantity of water exhaled in twenty- 

 four hours by the pulmonary surface of man.' The average of 

 the numerous experiments of Valentin^ is 5 40. grammes ; conse- 

 quently, very nearly the number indicated by Lavoisier and 

 Seguin. This quantity is besides very variable. It may be 

 augmented at will in animals, for example by injecting water 

 into their veins. 



Complex reactions take place in the blood, still as little known 

 as those which cause the elaborated sap in plants. The grand 

 fact is the fixation of oxygen ; but we have seen that there were 

 also the absorption and exhalation of azote. Lavoisier and Seguin 

 had already deduced from their observations that a portion of 

 the water exhaled by the pulmonary surface was directly formed 

 in the blood by the oxydation of the hydrogen. Modem obser- 

 vations have confirmed this view, which may, with great likeli- 

 hood, be extended to aqueous excretion in all its-forms ; for the 

 lung is only one of the numerous channels through which water 

 goes forth from animal organisms. 



The most complete researches have been made, touching the 

 physical phenomena of respiration, especially with regard to animals 

 having lungs, birds and mammifers ; but these phenomena, viewed 

 in a general mg-nner, differ little in branchial respiration. On the 



' Premier M4mm,re sur la TranspiratUm {Mimovres de VAccuUmie des 

 Sciences de Paris (1790), and Annales de Chi/mie, t. XC). 

 ' Leh/rhuch der Physiologie, t. I. 



