450 Historical 



tendency towards a vacuum produced in the pericardium and the 

 mediastinum during the inspiration, and intended to assist the concen- 

 tric effort of impulsion towards the heart, must be more pronounced. 

 (P. 52.) 



The book of Pravaz ends with the discussion of the favorable 

 effect of compressed air in the treatment of phthisis, rickets, chlo- 

 rosis, anemia, deafness, chronic congestions of the nervous centers, 

 and different neuroses. 



In explaining the numerous successes which he lists in this 

 connection, Pravaz gives especial emphasis to the effect of the 

 chemical reason of the superoxygenation of the blood, and the 

 greater activity thus imparted to the phenomena of metabolism. 

 But he likewise refers to the mechanical action, the pressure of the 

 compressed air. So, in speaking of the cure of coxalgia by the 

 compressed air bath, he says, in a work preceding the one from 

 which we have just quoted: 12 



In compressed air, one can carry out the indicated compression of 

 the swelling of the hip in the most uniform and harmless manner, 

 because not only the articular head but also the capsule, which pro- 

 jects abnormally out of its adherences, is pushed inward from without. 

 This compression, the force of which upon the area corresponding to 

 the cotyloid cavity can be reckoned as twenty kilograms per atmos- 

 phere, must cause the absorption, at least partial, of the liquids which 

 have escaped, as we see in cases of dropsy and hydrocephalus, when a 

 more or less tight bandage is placed around the abdomen or the 

 skull. (P. 8.) 



Further on, mentioning the case of a girl cured by compressed 

 air of a wryneck "due to cephalic hyperemia," he declares that the 

 freeing of the cerebrum is due to the mechanical pressure: 



The vacuum which is caused in the jugular veins during the 

 inspiration and which draws thither the blood from the head and the 

 spine tends to be filled more rapidly in proportion to the strength of 

 the outer pressure; and on the other hand, the increase of this pres- 

 sure must provide a greater obstacle to the ebbing movement which 

 the expiration causes in the afferent vessels; then we cannot be sur- 

 prised that the capillary system of the brain and the spinal cord, in 

 communication with the veins subjected to a sort of suction which has 

 become more vigorous than in the normal state, can free itself of the 

 excess of blood which choked it. (P. 13.) 



Pol and Watelle 13 are the first authors who have tried to explain 

 the symptoms of decompression, the time of which they had also 

 been the first to determine definitely. They are the ones who re- 

 ported to us .this characteristic saying of the workmen: "Pay only 

 when leaving." 



