302 THE ADRENAL, GENERAL MOTOR, AND VAGAL SYSTEMS. 



combinations extra cor pore; it doubtless does the same in the 

 gastric structures. But here conditions are especially well 

 adapted for such a reaction, if we analyze the question with 

 the aid of thermochemistry. Equal volumes of chlorine and 

 hydrogen can only be kept in an absolutely dark place; diffuse 

 light causes them to slowly unite, while a bright light sun- 

 light, for instance brings on such an instantaneous combina- 

 tion of the two elementary bodies that the flask containing 

 them flies into pieces. The fact that this may also be brought 

 on with a magnesium light which, as is the case with sunlight, 

 is rich in chemical rays, .indicates that we are dealing with a 

 process in which heat plays a predominant part. Precisely as 

 the sun sends radiations which the earth transforms into heat, 

 so does it, in the experiment mentioned, send radiations which 

 the combined chlorine and hydrogen transform into heat; the 

 mixture absorbs the undulations of the ether and transforms 

 them into molecular energy: i.e., heat. But a multitude of 

 familiar every-day phenomena prove that increased molecular 

 energy, or heat, may be procured without light-rays, etc.; the 

 mere rubbing of a match against a dry surface will cause it to 

 light, for instance. That this occurs without in the least in- 

 volving the need of a chemical body on the substance against 

 which the match is rubbed to start the reaction indicates that 

 friction causes increased vibratory activity in the ingredients 

 of the match-tip, and, these only combining when a given tem- 

 perature is reached, heat must obviously be accepted as the 

 causative factor of the process. Now, a very significant feature 

 in connection with the formation of the gastric hydrochloric 

 acid is the fact that the combination temperature, when an im- 

 mediate reaction is obtained between chlorine and hydrogen, is 

 39.5 C. (103.1 F.), while that of the gastric cavity is about 

 38 0. (1004 F.). The fact that the walls of the stomach, 

 the seat of the blood-flow, must show a higher temperature 

 than this (at least 2 degrees, that of the liver being 106 de- 

 grees) pointedly suggests that the formation of hydrochloric 

 acid only occurs when the stomach is brought up to the re- 

 quired temperature. 



How this occurs may now easily be surmised: (1) the ex- 

 trinsic vascular supply, under the constrict ive influence of the 



