328 PULMONARY MUCOUS TISSUE. 



to the existence ofapneumic acid (see p. 128) ; the existence 

 of this acid has not been confirmed ; and, moreover, it has 

 been observed that whenever, in the course of experi- 

 ments, the oxygen mingles with the venous blood, even in 

 vitro, carbonic acid is immediately evolved : this leads us to 

 imagine that the combination of the oxygen and the globule 

 (oxy-hemoglobin, the spectroscopic features of which we 

 have already studied, p. 119), possesses properties similar to 

 those of an acid, and thus occasions the evolution of carbonic 

 acid from the venous blood. The absorption of oxygen is 

 thus doubly important in respiration, both for its own sake, 

 and as the cause of the evolution of the carbonic acid pre- 

 viously formed. 



D. Asphyxia. 



The preceding remarks will enable us to point out, in a few 

 "words, the various methods by which asphyxia may be pro- 

 duced. Asphyxia may be caused, either by deprivation of 

 respirable air, or by intoxication, that is to say, by the 

 absorption of any pernicious gas. 1 



a. Asphyxia, caused by absence of respirable air, may be 

 produced in two ways, either by there being no oxygen to 

 be absorbed, or by the carbonic acid being no longer 

 evolved from the blood. 



1. Animals die in an atmosphere which is not constantly 

 renewed by the admission of fresh air, when they have ex- 

 hausted the greater portion of the oxygen, provided that the 

 carbonic acid formed be taken away, in order to avoid the 

 inconvenience produced by its accumulation; reptiles die 

 when all the oxygen is exhausted, the mammifera when only 

 2 per cent remain ; and birds, when there is only 4 or 3 per 

 cent of the quantity left (Paul Bert). These facts explain 

 the feeling of distress experienced by aeronauts and by trav- 

 ellers who ascend high mountains: the diminution of the 

 external pressure produces the same effect as rarefaction of 

 the oxygen; respiration is, consequently, performed with 

 difficulty, and there is a lack of oxygen for the purpose of 

 keeping up combustion, and for producing heat and force; 

 fatigue, chill, and a tendency to sleep, follow. These effects 

 are produced in an exaggerated degree while ascending 

 mountains, because the traveller is then obliged to exert 



1 See " Nouveau Diet, de Med. et de Chirurgie," Vol. III. art. 

 Asjihyxie, par P. Bert. 



