236 CHEMISTRY OF PLANT LIFE 



are extraordinarily sensitive to minute changes in the reaction of 

 the medium in which they are working. A change toward acidity 

 in protoplasm immediately results in the stimulating of carbo- 

 hydrate-splitting enzymes, which increases the supply of easily 

 oxidizable simple carbohydrates, thereby tending to compensate 

 for the decrease in respiratory activity. Further, increase in 

 acidity increases proteolysis, thereby liberating alkaline ammonia- 

 derivatives which tend to neutralize the rising acidity and so to 

 restore normal neutrality or alkalinity. Thus it will be seen that in 

 the very great sensitivity of its enzyme catalysts to slight changes 

 in the reaction of the medium, the protoplasm possesses a very 

 efficient mechanism for regulating changes and restoring equi- 

 librium, if the latter be disturbed by any abnormal conditions. 

 It should also be noted, at this point, that the almost universal 

 presence in protoplasm of salts of carbonic and phosphoric acids 

 acts as an additional " buffer " against pronounced changes in 

 reaction of the material; the bicarbonates acting by means 

 of their ready release or absorption of carbon dioxide, and the phos- 

 phates by their easy change from mono-sodium phosphate to di- 

 sodium phosphate, and vice versa, the former being slightly acid 

 and the latter slightly alkaline in reaction. 



A third effect of increasing acidity is that it induces increased 

 imbibition of water by the colloidal gel and causes swelling of the 

 tissue. After death, when the reaction of the protoplasm becomes 

 pronouncedly acid, this swelling often proceeds to the point of 

 rupturing of the cell-wall, or internal membranes of the proto- 

 plasm, thus permitting the entrance of the putrefactive bacteria 

 and hastening the decay of the tissue. 



Finally, comparatively slight variations in the reaction of the 

 protoplasm produce enormous changes in its colloidal condition, 

 affecting in a very marked degree its permeability, its power of 

 adsorption, etc. 



It is clear, therefore, that variations in the chemical reaction of 

 protoplasm profoundly affect its colloidal condition, its enzymic 

 activity, and its respiratory processes. This necessarily brief 

 survey is sufficient to indicate how important to the activity of the 

 protoplasm is the chemical reaction of the material, and the 

 mechanism with which it is provided for maintaining the favorable 

 condition of neutrality or slight alkalinity. 



