CH. ii] THE CHARACTERS OF BACTERIA 17 



It is well known that B. diphtheriae produces toxins more 

 plentifully in a free supply of air (Clark, 1910). 



The bacillus of malignant oedema is said to lose virulence 

 when grown aerobically (Harass, 1906) and that of cholera to 

 gain virulence when grown anaerobically (Hueppe, quoted by 

 Adami, 1892). 



Foa (1890) describes how a strain of the pneumococcus 

 could by anaerobic growth be deprived of its property of 

 causing a characteristic inflammatory oedema of the skin 

 when injected into an animal. 



Wood (1889) attributed the diminished infectivity of 

 virulent organisms discharged from the bowel in many 

 diseases to the fact that in the bowel they are practically 

 deprived of oxygen. 



(f) Bright sunlight destroys the virulence of some patho- 

 genic organisms (Marshall Ward and Blackmail, 1910) and 

 leads to the loss of pigmentation in others (Laurent, 1890). 

 The bacterium mycoides, on the other hand, will only produce 

 its red pigment in the dark (Scholl, quoted by Wood, 1889). 



5. Exposure to the ultra violet rays has recently been 

 shown by Madame Henri (1914) to effect a startling change 

 in both the morphology and the pathogenicity of B. anthracis. 

 Cocci and filamentous forms were produced which differed 

 from the original bacilli in their power of retaining stains, 

 of forming spores, of liquefying gelatine and coagulating milk, 

 and which gave rise, on injection into an animal, to symptoms 

 quite unlike those produced by normal anthrax bacilli. The 

 new forms did not revert after daily subculture for over two 

 months. 



1 6. Electrolysis. Electrolysis may produce changes in the 

 morphology and staining properties of bacteria. Russ has 

 observed the production of elongated forms of B. coli, with 

 altered reaction to Gram's stain, in urine (within the human 

 bladder and outside the body) as a result of the passage of 

 a galvanic current of T 1 5 th m.a. strength for one hour. The 

 modification persisted for many months. 



7. The age of the culture is of importance in the case of 

 many pleomorphic organisms. For example, B. megatherium 



D. 2 



