RESPIRATION 



143 



them. They are specially liable to occur at night. The rapid 

 breathing is apt to produce the impression in a physician that it is 

 the heart and not the breathing, that has failed ; and this impres- 

 sion may be apparently confirmed by the presence of secondary 

 anginal pain. In all doubtful cases, the effects of properly admin- 

 istering oxygen will decide the diagnosis. If the immediate cause 

 of the symptoms is failure of the respiratory center, the effects 

 of the oxygen are rapid and prompt, and have been so in cases 

 which have chanced to come under my own observation. 



It is evident that anoxaemia caused by irregular distribution 

 of oxygen among the lung alveoli may be due to a variety of 

 causes. One of these is emphysema ; for the emphysematous parts 

 of a lung will naturally be supplied with far more than the proper 

 proportion of air to suit their greatly diminished respiratory 

 surface, while the other parts will receive correspondingly less 

 air. The arterial blood will thus be a mixture of over-arterialized 

 I 2 



llllllllllltllllllllllllllllllllllllllM 



Figure 47. 



Subject J. S. H. Rebreathing in and out of 50 liter cylinder. Time marker = 

 2 seconds, i. Sitting. 2, Lying. 



and under-arterialized blood, with resulting anoxaemia, which 

 may or may not be compensated by one or other of the processes 

 to be described in succeeding chapters. 



Another cause of the same general character is bronchitis or 

 asthma. The irregular partial blocking or muscular constriction 

 of the bronchi and bronchioles in these conditions must lead to 



