HERMANN VON HELMHOLTZ 



hydrodynamics, investigating and measuring the force 

 and frequency of the heart's contractions, and deter- 

 mining the causes of the high pressure maintained in 

 the arterial system, the nature of the pulse, and the 

 uniform flow of the blood in the capillaries. These 

 investigations are all of a physical character. Finally, 

 if the physiologist pursues his analysis still farther, 

 he may examine the chemical characteristics of the 

 tissues forming the heart and vessels, the nature of 

 chemical compounds, both organic and inorganic, 

 existing in these tissues, and the influence of chemical 

 substances upon the living heart. Almost every 

 physiological problem may be attacked in a similar 

 way, and it can only be fully solved when all the 

 information derived from anatomy, chemistry and 

 physics is brought to bear upon it. It will also be 

 evident that some physiologists are attracted to one 

 aspect of the subject, while others are drawn to 

 another. One man endeavours to explore the mystery 

 of living action by the microscopical examination of 

 tissues, living and dead ; another works at the chemical 

 constitution of organs and tissues, and tries to get a 

 glimpse into the nature of the chemical processes 

 associated with life ; while a third investigates the 

 phenomena as special problems in physics. Helmholtz 

 was an outstanding representative of the latter class, 

 and he was so largely by reason of his special aptitude 

 for physical and mathematical research, and of his 

 surroundings. He might properly be described, even 

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