CHARACTERS OF ORGANISMS. 23 



These complex associations of many atoms of carbon with many 

 atoms of other elements, are readily dissociated when exposed to 

 the air under even slightly disturbing influences. When heated 

 to a certain degree they burn, i.e., unite rapidly with the oxygen 

 of the air, and in the presence of minute organisms they putrefy. 

 Thus instability is a general feature commonly met with in most 

 substances of organic origin. 



Chemical instability reaches the highest pitch in tissues which 

 are actually alive and engaged in vital processes. So long as any 

 texture lives it must constantly undergo certain chemical changes, 

 one of which is regarded as a kind of decomposition, tending to 

 produce disintegration, and the other, a re-integration by means 

 of new chemical associations with fresh materials. A tissue may 

 then be said to deserve the term living, only as long as it under- 

 goes these antagonistic chemical changes. The tendency to de- 

 structive oxidation or disintegration is intimately connected with 

 the functional activity of the living texture and increases with 

 this activity. The re-integration or constructive process requires 

 the presence of suitable materials with which. the texture may 

 combine, in order to make up for the loss. Thus living tissues 

 are ever on the point of destruction, which can only be warded 

 off by the timely reconstruction of their chemical ingredients by 

 suitable fresh materials. This reconstruction by means of fresh 

 matter from without is called assimilation, and forms the most, if 

 not the only, satisfactory criterion by which adequately to dis- 

 tinguish living beings from inorganic matters. 



The whole object of all these chemical processes is to supply 

 suitable fresh materials to the various textures for their assimi- 

 lation. This will be found to form a great part of physiological 

 study. Further, the energy manifested in the living activity of 

 the textures depends upon the various oxidizing processes, and 

 the exact laws which govern these combustions, and the results 

 they give rise to in the various tissues, practically make up the 

 other part of physiology. 



3. Vital Phenomena. The so-called vital phenomena 

 which take place in the textures of organisms are, for the most part, 



