BACTERIA 509 



animal kingdom, and that an acid medium, general in the 

 vegetable kingdom, was inimical to their development. In 

 spite of this generalisation, it is now well known that bacteria 

 are the primary cause of several of the most destructive of plant 

 diseases. This knowledge we owe more especially to the valu- 

 able research conducted by Dr. Erwin F. Smith, director of the 

 Laboratory of Plant Pathology, U.S. Dept. of Agriculture. 



Smith, Erwin F., Bacteria in Relation to Plant Diseases, 

 vol. i. (1905). 



Potter has recently stated that bacteria are active agents 

 in the oxidation of amorphous carbon. His summary on the 

 subject is as follows : 



Under conditions of exposure to the air, a slow oxidation 

 of amorphous carbon takes place through the agency of 

 bacteria. This has been conclusively established by experi- 

 ments upon such carbonaceous substances as charcoal, lamp- 

 black, coal, and peat. 



When these substances are subjected to bacterial action 

 carbonic acid is given off, as estimated volumetrically by 

 absorption in baryta solution and titration with standard 

 oxalic and hydrochloric acids. 



The amount of CO 2 given off increases in proportion to 

 the rise of temperature and ceases to be evolved at a supra- 

 vital temperature. There is no evolution of CO 2 under 

 perfectly airy conditions such as preclude the possibility of 

 bacterial life. 



A distinct rise of temperature occurs through the action 

 of bacteria. The heat generated was determined by 

 measurement, with a galvanometer of the electromotive force 

 produced by the difference of temperature between two 

 thermo-elements, one placed in a sterile and the other in an 

 inoculated flask. 



The evolution of CO 2 and the accompanying rise of tem- 

 perature does not take place when carbonaceous substances 

 are preserved from the intrusion of micro-organisms. 



The heat generated by microbial activity is an influence to 

 be taken into account in connection with the oxidation and 

 spontaneous combustion of coal ; it may be a dangerous 

 motive force acting upon explosive gases. 



The oxidising action of bacteria must be largely responsible 

 for the disintegration of coal and the high percentage of 

 depreciation which it undergoes in store. 



