428 Historical 



begin to rise gradually during the period of constant maximum 

 pressure, without reaching its original height, however. 



Moreover, the changes which the pulse undergoes here are ex- 

 plained by and are perceptible to the touch, because in most cases the 

 pulse which is normal before the entrance into the pneumatic ap- 

 paratus is almost imperceptible to the touch of the finger in com- 

 pressed air; it is really the pulsus debilis. We should note in regard 

 to this last point that the changes of the pulse described above 

 in a pulsus longus, such as we have seen appear in the pneumatic 

 apparatus, and Which are observed in normal air pressure in certain 

 morbid processes, such as aneurisms and embolisms, give a deceptive 

 sensation to the finger, so that even when the vertical height of the 

 pulse remains identical, as Marey observed (p. 243), the pulse will ap- 

 pear stronger in proportion as the blood wave is more gradual, which 

 is expressed by the rise and fall of the blood pressure in the vessels; 

 but since in our case, in compressed air, the decrease of the strength 

 of the pulse indicated by touch is also confirmed by the decrease in 

 vertical height of the tracing, the decrease of the strength of the 

 pulse in itself must be considered certain. 



We should now have to show the cause of this decrease of the 

 strength of the pulse in compressed air, as it appears from our re- 

 searches; we might well think first of the weakening of the action of 

 the heart itself, and of the occasional circumstance of the decrease 

 of the strength of the pulse in compressed air, a weakening which 

 perhaps is caused by the rise in resistance, which the increase of 

 the atmospheric pressure, compressing the whole of the peripheral 

 vessels, produces in the arterial system; in support of this hypothesis 

 we might mention data which I reported under other circumstances 

 and in another place; in fact, inspection and palpation of the heart 

 show its weaker impulse; auscultation of the heart gives an identical 

 result, and the sound appears further away, so to speak. 



However, these data in no way show and prove that a change 

 has taken place in the strength of the heart impulse, for, on the one 

 hand, we find it extremely difficult to get an almost certain and 

 demonstrated proof of the changed intensity of the contraction of the 

 heart, and, on the other hand, the weakening of the heart impulse 

 and of the heart sounds, noted by sight, hand, and ear during the stay 

 in compressed air, can be only apparent; and, as I have already shown 

 in the dissertation mentioned above, can be only a simple effect of a 

 displacement of the heart, caused by the compression of the air and 

 connected with the increase of the capacity of the lungs and the pass- 

 ing of the anterior layer of the left lung in front of the heart. (P. 564- 

 567). 



So far we have discussed only the form of the isolated wave, with- 

 out taking into account the combination of the successive waves, and 

 yet this complex phenomenon requires some explanations. 



Let us draw a line from the beginning to the end at the base 

 of the wave or across its apex; we shall then have what Marey called 

 a line of the whole (gemeinsame linie), which may give us some in- 

 formation about certain changes in the pressure of the blood and in 

 the distention of the vessels. This line which, as we have said, varies 



