1014 Summary and Conclusions 



I had the satisfaction of receiving the following note shortly after 

 from one of the executives of the company: 



We have transmitted to our Aalbert Works the information you 

 gave us about the precautions to be taken for men working at high 

 pressures. 



We have exceeded the depth of 32 meters below the level of the 

 water, and the symptoms disappeared when the time in the exit lock 

 was increased. 



2. Low Pressures. Medical Apparatuses. 



The effect of low pressures has given rise to only a small number 

 of articles in recent years. But two of them are of considerable 

 importance from the theoretical point of view. 



M. J. Pravaz, August 9, 1875, sustained a thesis before the 

 Faculty of Science of Lyons on the effects of an increase of atmos- 

 pheric pressure, in which he considers successively the circulation, 

 the respiration, and the nutrition. 



In regard to the first of these functions he notes, like all former 

 observers, a certain slowing of the pulse during a stay in compressed 

 air, and he explains it: (1) by the increase in the temperature of 

 the body, acting secondarily upon the heart; (2) by the increase of 

 the arterial tension. The latter is supposed to be caused by the 

 direct obstacle to the course of the blood occasioned by the com- 

 pressed air acting to "drive back from the peripheral parts the blood 

 of the capillaries and veins (p. 23) ." We see that M. Pravaz accepts 

 the theory of superficial crushing in compressed air; he considers 

 as proof the strange experience of Vivenot which we reported 

 above and rated at its true value. We do not think it worth while 

 to repeat the refutation of these errors. 



The respiration, he says, becomes both less frequent and more 

 ample, at least in the neighborhood of a half-atmosphere of com- 

 pression; beyond (M. Pravaz goes only to two atmospheres), there 

 is a movement in the opposite direction. The explanation of these 

 data is the one which Ch. Pravaz (p. 447) had already given, whose 

 opinions his son adopts on all points. The variations in the ampli- 

 tude have been measured by the aid of the anapnograph of MM. 

 Bergeon and Kastus: if the extent of respiratory movement at 

 normal pressure is expressed by 100, it becomes 106 at a pressure of 

 19 cm., 118 at 38 cm., 109 at 76 cm. But M. Pravaz did not seek to 

 study the relation between the frequency and the amplitude, so as 

 to determine the variations in the output, in the pulmonary ventila- 



