Theories and Experiments 457 



Their method of production is easily ascertained; in fact, we know 

 that the increase of the pulmonary capacity is very great under the 

 influence of compressed air; that the cells of the respiratory organs 

 are considerably distended: at the time of leaving the caissons and 

 especially after a hasty and poorly managed decompression, a vacuum 

 is too quickly made in the thoracic cavity, and this vacuum must nec- 

 essarily be replaced by a speedy afflux of blood and the other liquids; 

 hence these congestions; hence also this spitting of blood, as a result 

 of the rupture of vessels in the pulmonary parenchyma. 



Therefore one may understand that full-blooded, plethoric persons 

 are more subject to these affections than persons with lymphatic or 

 nervous temperament. 



The cerebral symptoms, examples of which we have mentioned, 

 are also in his opinion the result of congestions. And here, M. 

 Franqois tries to explain why they appear exactly at the time of 

 decompression: 



It is undeniable that these cerebral congestions, like those of the 

 pulmonary tissue, do not result from the same causes as congestions 

 attacking persons in the course of ordinary life, in which they are 

 produced generally by a stasis of venous blood occasioned by an 

 obstacle to the return of the blood; at other times, but less frequently, 

 they are the result of a great arterial impulse; but then there always 

 occurs a subsequent stasis which may become harmful when the 

 congested blood changes from red to dark and becomes a depressant, 

 that is, when it becomes less and less rich in oxygen. 



Is the same thing true in congestions produced by compressed air? 

 Evidently not, for here there is no congestion as long as the increased 

 atmospheric pressure lasts; then when the workman leaves the in- 

 creased pressure, the excess of air contained in his body seeks to 

 establish an equilibrium with the outer air; this tendency operates 

 immoderately, as would be expected; hence, a surge of blood, but a 

 red blood, towards the nervous center, a surge which sometimes is 

 overpowering, especially if the decompression has not been made 

 gradually and carefully, but which up to the present has not produced 

 any fatal case. 



In all cases, when the patient was bled, the blood issued from 

 the vein very red; no dark blood has been observed in bleeding. 

 (P. 313.) 



Finally paraplegias, retention of urine, etc., would be due to 

 medullary congestions produced by a similar cause. 



It is likewise, as we said, upon the workmen employed at the 

 bridge of Kehl that M. Bucquoy 19 made his observations. His work 

 is extremely noteworthy, especially from the point of view of 

 physiological explanations. , 



He first discusses the increase in the quantity of oxygen con- 

 tained by the blood. But the hypothesis which might have ap- 



