30 THE ACTIVE FORCES OF LIVING ORGANISMS 



Every increase in the amount of oxygen in a tissue 

 leads to, or is accompanied by, expansion, whilst 

 every decrease in the amount of oxygen in a tissue 

 leads to contraction. The presence of carbonic acid 

 in the tissues is also probably a stimulus to con- 

 traction. 



The mode of vibration of the molecules of nerve- 

 cells depends on the manner, degree, and frequency 

 with which the variations in the state of oxidation of 

 the tissues are produced. Excessive oxidation causes 

 relaxation. 



The period and degree of action and reaction of all 



drugs varies, firstly, according to their composition, and, 



secondly, according to the habitual mode of vibration 



of the molecules in the nerve-cells of the individual. 



Tte If you scrape some of the gray matter from the 



apparent . ^ . . ° •' 



effect of brain of an animal which has been recently killed, 



drugs on 



the gray and tease one portion of it on a glass slab or small 

 dish with water, another with a weak solution of 

 acetic acid, and a third with a fairly strong solution 

 of strychnine, you will notice that the first of these 

 is more milky in appearance than the other two ; 

 and whilst the cells in the watery specimen show a 

 tendency to dissolve and become fused, those in the 

 strychnine and acetic acid are inclined, if anything, 

 to contract and appear curdy or caked. Under the 

 microscope the three specimens give corresponding 

 results, a strychnine preparation being especially re- 

 markable for the sharpness of the outlines of the 

 nerve-cells and of their granular contents. If, again, 



