MOVEMENTS OE RESPIKATION ON THE CIRCULATION OF THE BLOOD. 573 
in Moleschott’s ‘Untersuchungen’*. Of these experiments, which were performed in 
Ludwig’s laboratory, and apparently at his suggestion, there were two series. The first 
related to the effect produced by the artificial production and maintenance for various 
periods in the air-tubes of pressures which either exceeded or fell short of the pressure 
of the atmosphere by several inches of mercury. The second series, which alone directly 
concerns the present inquiry, consisted of experiments with the kymographion, in which 
either the movements of the thoracic walls or those of the respired air were recorded 
on the cylinder simultaneously with the variations of arterial pressure. The animals 
employed (dogs) and all the other conditions were the same as in the previous experi- 
ments of Ludwig, and the difference in the mode of recording was insignificant. The 
arterial tracings were of the same form as those obtained by Ludwig, but the relation of 
the arterial to the respiratory wave was such as to lead Einbrodt to opposite conclusions. 
According to Einbrodt, “ the mean arterial pressure is slightly diminished at the very 
commencement of inspiration, but immediately afterwards gradually and constantly 
rises, while the action of the heart is accelerated. The pressure continues to rise until 
the beginning of expiration, when it reaches its maximum. Thereupon a pause is usually, 
but not constantly, observed in the contractions of the heart, in which of course the arterial 
pressure sinks considerably. It always happens that during the remainder of expiration 
the pressure is diminished while the action of the heart is retarded.” 
The only other observations by which our knowledge of this subject has been mate- 
rially advanced are those of Marey, made with the aid of the instrument invented by 
him, and described in his work on the Physiology of the Circulation, under the name of 
“ Sphygmographe. ” By this instrument, the purpose of which is to measure the arte- 
rial tension in the living human subject and to record its rhythmical changes by mecha- 
nical means, a tracing may be obtained (provided that the individual under observation 
breathes largely or with effort) which exhibits characters essentially the same as those 
described by Ludwig, that is to say, by taking corresponding points in a series of arte- 
rial oscillations and connecting them with each other, a curve is produced consisting of 
larger waves, which are in relation with the thoracic movements. Marey found that the 
nature of this relation differs according as the individual breathes with widely open or 
partially closed respiratory apertures. When respiration is performed largely and with- 
out obstruction, the ascent of the respiratory wave coincides with inspiration, the descent 
with expiration ; whereas when the movement of air is obstructed by the narrowing of 
the air-channels, and each respiration is performed with great effort though with little 
effect as regards the quantity of air introduced, the curve descends in inspiration, 
ascends in expiration. These differences Marey thus explains: in free breathing the 
diaphragm presses on the aorta and thereby increases the arterial pressure. In restricted 
breathing the movement of the diaphragm and consequently its influence is diminished, 
while on the other hand those changes of tension in the thoracic cavity, which under 
* “ fiber den Einfluss der Athembewegungen auf Herzseblag 'und Blutdruck,” Moleschott’s Untersucb. 
B. vii. 1860. 
4 I 2 
