RESPIRATION OF DIFFERENT GASES. 



737 



a point is reached at which the partial pressure of oxygen becomes 

 dangerous to life. When the arterial blood contains a third more than 

 its normal quantity of oxygen, the metabolism of the body diminishes 

 greatly, and the animal dies. The following examples will illustrate 

 this effect : 



The practical importance of these experiments in connection with the symp- 

 toms observed in men after working in caissons is obvious. Details of numer- 

 ous cases are given by Paul Bert 1 and others, 2 but here it is sufficient to draw 

 attention to the chief symptoms and changes observed in men working in 

 compressed air. The earliest and most constant symptom is pain and noise in 

 the ears, due to the pressure upon the tympanum ; relief is generally obtained 

 by swallowing, or by a forced expiration with closed nose and mouth ; in some 

 cases, however, the tympanum has been ruptured. The respiration is slower 

 and deeper. The danger to life, however, chiefly occurs when the workmen 

 leave the caisson and come out into the fresh air ; the symptoms then observed 

 are due to the relative fall in atmospheric pressure, and are chiefly these 

 very painful itching of the skin, painful swelling of the muscles and joints, 

 disturbances in locomotion and sensation, paralysis of the lower limbs, 

 bladder, and rectum, and more rarely extensive paralysis, unconsciousness, 

 and sudden death. 



1 Loc. cil., p. 369. 



2 See ref. given by Paul Bert, loc. cit. ; E. H. Snell, "Compressed Air Illness or so- 

 called Caisson Disease," London, 1896 ; Heller, Mager, Schrotter, Centralbl. f. PhysioL, 

 Leipzig u. Wien, 1896, No. 2, S. 40 ; Friedrich and Tauszk, Wien. klin. fiundschau, 1896, 

 S. 233. 



VOL. I. 47 



