GENERAL MORPHOLOGY AND PHYSIOLOGY. 



Electricity. Cohn and Mendelsohn found that 

 a constant galvanic current produced a deleterious 

 effect owing to electrolysis. At the positive pole 

 the liquid became distinctly acid, and at the 

 negative pole distinctly alkaline. With a weak 

 current there appeared to be no effect, two power- 

 ful cells at the very least being necessary. 



Light. Downes has shown that sunlight is fatal 

 to putrefactive bacteria. This is believed to be 

 due to a process of induced hyper-oxidation, from 

 which living organisms ordinarily are shielded by 

 protective developments of the cell-wall, or of 

 colouring matter, which cut off injurious rays. 

 Duclaux has investigated the same subject, and 

 observed that micrococci were more sensitive to 

 sunlight than the spore-bearing bacilli. Engel- 

 mann has described a bacterium whose movements 

 cease in the dark, and Zopf states that in his 

 cultures of Beggiatoa roseo-persicina the growth was 

 much more strongly developed on the side of the 

 vessel facing the light. 



Chemical reagents. Many substances, such as 

 carbolic acid, corrosive sublimate, chlorine, bromine, 

 etc., have a marked effect upon the growth of 

 bacteria. This will be more fully described in 

 another chapter. In several cases the bacteria 

 themselves secrete a substance which is injurious 

 to their future development. 



Products of growth. Bacteria may be 

 grouped together according to the changes pro- 



