November 19, 1915] 



SCIENCE 



703 



Stephen Hales, a Church of England 

 clergyman, who tied into the femoral artery 

 of the horse a glass tube nine feet high and 

 noted the height to which the blood rose. 

 He was able to report an average pressure 

 of the blood in the artery sufficient to sup- 

 port a column of liquid eight feet three 

 inches in height, while the blood rose at the 

 same time to less than one foot in the corre- 

 sponding vein. He observed also fluctua- 

 tions in pressure due to the individual heart 

 beats, to the movements of respiration and 

 to other causes. The details of his experi- 

 ments were communicated to the Royal So- 

 ciety of which he was a fellow and were 

 published in 1733 in a work entitled 

 "Statical Essays, Containing Haemo- 

 staticks. " 



The method employed by Hales was ex- 

 tremely inconvenient on account of height 

 of the tube. Moreover, it introduced a 

 greatly disturbing factor, namely, the loss 

 of blood from the vessels of the animal into 

 the tube. These inconveniences were over- 

 come by the use of the mercury manometer 

 by Poiseuille (in 1828). But the careful 

 and detailed study of blood pressure dates 

 from the invention by Ludwig (1847) of 

 an exact method of recording blood pres- 

 sures. From that time onward, not only 

 in Ludwig 's laboratory where many of the 

 generation of physiologists just passing 

 were trained in the methods of their sci- 

 ence, but in all the physiological labora- 

 tories of the world has the study of blood 

 pressure been continued. 



It is impossible here to summarize all the 

 facts of importance that have been the out- 

 growth of these investigations, and of 

 others, connected with the functions of the 

 circulatory system, and which could have 

 been learned in no other way than by 

 experiments on living animals. 



The heart is a pump driving an incom- 

 pressible liquid through a completely closed 



system of branching elastic tubes, the 

 terminal connections of the outflow and in- 

 flow portions of the system being all of 

 capillary size. The study of this system 

 presents a series of difficult problems in 

 hydrodynamics, in which all the relations 

 of force, rate and output of the pump, the 

 heart, and the pressure, and friction condi- 

 tions in the arteries, veins and capillaries 

 must be considered. 



But this machinery is all composed of 

 living tissues which are interacting and 

 self regulatory to an extraordinary degree. 



The discovery by Claude Bernard, and 

 others, of the existence of vasomotor 

 nerves through which the caliber of the 

 arteries may be changed, regulated and 

 controlled, thus adjusting the resistance to 

 the ability of the heart, and also providing 

 that the heavier flow of blood may be 

 shunted from one set of organs to another 

 according to the needs of the body, is of 

 prime importance ; so also was the discovery 

 by Weber of the inhibitory action of the 

 vagus nerve upon the heart, which, acting 

 like a brake on that organ, keeps its action 

 always under definite control; and the dis- 

 covery by V. Cyon of the accelerator nerves 

 whose function is in direct opposition to that 

 of the vagus. Further, v. Cyon found that a 

 special nerve, the depressor, carrying im- 

 pulses from the heart and the great blood 

 vessels to the brain, causes, when exjcited, 

 a dilatation of the peripheral vessels and 

 consequent reduction of the pressure 

 against which the heart must work. None 

 of these things could have been guessed 

 from the study of the anatomical struc- 

 tures, nor could ever have been found out 

 in any other possible way than by experi- 

 ments on living animals. 



But it may be asked. Has this knowledge 

 any value? Has it any practical applica- 

 tion? Is it useful only for the gratifica- 

 tion of mere curiosity? 



