METHODS OF PHYSIOLOGICAL RESEARCH 29 



already accomplished in the direction of its established goal, and 

 to inquire by what path it may reach this goal. 



A. THE PAST ACHIEVEMENTS OF PHYSIOLOGICAL RESEARCH 



The aim of Physiology is to explain vital phenomena, i.e., to 

 discover their elementary causes, to put them into causal relation 

 with one another, to see whether their elementary causes are the 

 same as those of the phenomena of inorganic nature. What has 

 been accomplished in this direction ? 



The answer brings little encouragement, for, when the various 

 branches of physiology are carefully reviewed, it is found that 

 thus far practically nothing has been learned beyond the gross 

 mechanical and chemical activities of the vertebrate body. The 

 causes upon which these activities depend are, for the most part, a 

 complete puzzle. 



We know that respiration depends upon the laws of aerodynamics; 

 by the rhythmic diminution and increase of pressure of the air in 

 the lungs, as a result of the contraction and relaxation of the 

 respiratory muscles, the air streams passively in and out ; oxygen 

 is removed from it by the red corpuscles of the blood and is 

 chemically united with the substance of the corpuscles. But we 

 have scarcely an idea as to how the contraction of the respiratory 

 muscles comes about, or what events call forth the change of form, 

 termed contraction and relaxation, and the performance of work in 

 the individual muscle-cells. 



We know that the circulation of Hood in our bodies follows the 

 laws of hydrodynamics, that it is conditioned by the rhythmic 

 variation of differences of pressure within the vascular system, 

 which are brought about by the contraction and relaxation of the 

 heart-muscle. We have here again exactly the same problem as 

 in respiration, for, although Engelrnann has recently proved that 

 the causes of the rhythmic contractions of the cardiac muscle lie 

 in the living substance of the muscle-cells, as to the manner in 

 which the contractions come about physiology has enlightened us 

 very little. 



We know that the digestion of the ingested food takes place 

 strictly in accordance with chemical laws ; the chemical substances 

 secreted by the gland-cells of the digestive canal transform the 

 food chemically, exactly as we can imitate the processes by the 

 help of those digestive secretions outside the body in the test- 

 tube. But physiological chemistry leaves still unexplained how 

 the gland-cells come to secrete their specific substances, why the 

 cells of the salivary glands produce only ptyalin, and the cells of 

 the gastric glands only pepsin, although the same food is brought 

 to both by the blood. 



We know that in resorption the food-stuffs, changed chemically 



