FERMENTS, ENZYMES, TOXINS AND PTOMAINS 57 



a time, varying with the intensity of its Hght. Growth will 

 occur in the shaded part, none or only relatively little in 

 the illuminated part of the plate. 



Influence of Pressure. — ^The influence of pneumatic pres- 

 sure on the viability of bacteria appears to depend upon the 

 character of the gas used. Ordinary air, or its constituents, 

 oxygen and nitrogen, whenever pressed heavily (600 to 

 2000 atmospheres) upon cultures of bacteria, have a slight 

 inhibitory effect. Carbon dioxide under five to ten atmos- 

 pheres pressure is shown by Park and his associates to 

 destroy almost all of the typhoid, dysentery, diphtheria 

 and colon bacilli exposed to it within twenty-four 

 hours. 



Effect of Moisture. — ^As is the case with all living plants 

 a degree of moisture is essential to life. Certain species of 

 bacteria are killed by ordinary drying, and many of them by 

 absolute drying. The spores (to be described later) of bac- 

 teria are not so effected, a few species retaining their power 

 to germinate after having been dried, as the word is ordinarily 

 understood, for a comparatively long time, and spores have 

 been kept in a dry state for years without losing their power 

 to germinate. 



Influence of Electricity.- — ^The methods employed for 

 deciding this point have led to results that are inconclusive 

 and not easy of interpretation. 



It is true that when bacteria are exposed to the electric 

 current they are often inhibited and sometimes killed. 



This result may be interpreted in several ways, viz. : The 

 elevation of temperature caused by the current may explain 

 the destruction; the electrolytic action of the current on 

 matters in which the bacteria are located may, by dissocia- 

 tion, liberate agents that are destructive to bacteria, or a 



