474 Historical 



as great as that produced in laborers working six to eight hours a 

 day under a pressure of three to four atmospheres, the replacement 

 of the materials consumed cannot be made completely, combustion 

 will necessarily take place at the expense of the body, which will 

 cause loss of weight. 



We have quoted above (page 423 et seq.) the most interesting 

 parts of the long study made by Vivenot of the changes which 

 compressed air causes in the circulation and particularly in the 

 characteristics of the pulse. 



He asked himself whether these changes in the form of the 

 pulse can be explained by the direct, local action of the pressure 

 on the arterial system. To get the answer to this question, he car- 

 ried out the following experiment, in which he eliminates, he says, 

 all the complex elements of the problem, in order to concentrate 

 on "the contractility of the vessels and the pressure of the blood": 



A rubber balloon with a tube about 50 centimeters long is filled 

 with water, without being stretched, and the end of the tube is tied 

 shut with a thread. The heart is represented by the balloon, the 

 arteries by the tube, and the blood by the water. 



A sphygmograph is placed over the tube. A weight falls regularly 

 and always from the same height upon the balloon, representing in 

 this way the impulse of the heart. Thus a sphygmographic tracing is 

 obtained. 



At normal pressure, this tracing displays the characteristic appear- 

 ances of the normal pulse under these conditions: rapid, vertical 

 ascent, acute apex, descent in the form of waves, all the signs of weak 

 tension in the vessels. 



If the apparatus is placed in compressed air, nothing else being 

 changed, the curve of the sphygmograph is much altered. It then 

 resembles very closely the tracing given by the pulse itself under 

 compression. The line of ascent has become oblique, the apex has 

 changed into a plateau, the height of the impulse is only half as great, 

 and the polycrotism of the descending line has disappeared completely. 



When the weight is allowed to fall from a greater height, so as to 

 have a stronger pressure upon the artificial heart, the line of ascent 

 will become straighter, the amplitude of the oscillation will increase, 

 but there will be no polycrotism. If the apparatus remains a long 

 time in compressed air, a few drops of liquid will escape near the 

 ligature, a thing which never happens at normal pressure. At this time, 

 the sphygmograph gives a tracing which is very similar to that 

 obtained with the first impulse. 



On return to normal air, the original curve appears again, except 

 with a still steeper ascent and a more pronounced polycrotism. 

 Zur Kenntniss, etc., P. 373-374.) 



He concludes from this experiment and from the similarity of 

 the tracings obtained both from the arteries and with his apparatus, 

 in compressed air, that: 



