I goo- 1.] Observations on Blood Pressure. 189 



The Normal Effects of Gravity. 



It has long been known clinically that the circulation of the blood is 

 affected by the posture of the body, and that in weakened states of the 

 circulation the blood and other fluids, obeying ordinary hydrostatic laws, 

 tend to accumulate in the most dependent parts of the body. Further, 

 it had been noted that if the posture of the body be suddenly altered, 

 e.g., if a person be raised from the horizontal to the erect posture, the 

 inertia of the blood tends to make it lag, and as a result the upper pole 

 of the body, including the brain, temporarily becomes more or less 

 bloodless, and in consequence the individual may actually faint. This 

 method of inducing insensibility was actually employed by a Parisian 

 surgeon, who then operated upon his patient, rendered thus insensible to 

 pain. George Hayem^ writes as follows : " Phlebotomists had known 

 for a long time the influence of position on the production of syncope 

 when Piorry instituted his experiments on the subject. He bled some 

 dogs upright, and they fell at the end of a certain time into a sort of 

 state of dissolution with suspension of respiration. He stopped the 

 haemorrhage then and placed the animal head downwards, and immedi- 

 ately it breathed again. Often the same experiment could be repeated 

 many times on the same dog. I repeated the experiments in 1880 and 

 found them to be perfectly correct." It has constantly been observed, 

 moreover, that some individuals are much more susceptible to such 

 changes of posture than others, and that almost any person if temporaril)- 

 weakened in any manner, will tend to suffer from dizziness or even 

 faintness on suddenly assuming the erect posture. 



The effects of different postures and of sudden and gradual 

 alterations of these, have of late years been studied more accurately in 

 animals by means of tracings of the blood pressure. The very beautiful 

 tracings put on record by the 2nd Hyderabad Commission- on Chloroform 

 are examples of these observations, and more recently Mr. Leonard Hill 

 has added some of the same nature. My experiments were done on 

 dogs, with the exception of a few upon cats, and they confirm largely 

 what has already been observed and recorded. In each case the animal 

 was secured in a trough which was so constructed that it could be swung 

 into any angle with the horizon, with the canula in the arter}^ always 

 remaining in the axis of rotation. The canula was further carefully 

 kept at the same level as the manometer. Unless for some special 

 reason the canula was always placed in the proximal end of the left 



I ■' Death from Haemorrhage," Archive de Physiologie, 1888, p. 102. 



