78 BACTERIOLOGY 



persistent odor of formalin may be removed by fumes of 

 ammonia. 



Aniline Dyes. — Many of the aniline dyes, notably pyoktanin 

 (methyl- violet), possess germicidal properties. Malachite green 

 is said to possess even greater germicidal value than pyoktanin. 

 Methylene blue also possesses considerable germicidal power. 



Alcohol is a germicide of moderate power. It has little 

 effect upon spores but in concentrations of from 50 to 95 per cent 

 it destroys vegetative bacteria in a few minutes. 



Germicides destroy bacteria, as a general rule, because they 

 are general protoplasmic poisons, destructive to all living matte'r. 

 There is, nevertheless, some selective action. Thus, formal- 

 dehyde kills bacteria but has little poisonous effect upon injects, 

 such as mosquitoes, bedbugs, roaches or fleas. Mercuric chloride 

 is rapidly fatal to bacteria when it comes into contact with them, 

 but it has no very immediate destructive effect upon fly larvae 

 (maggots). Some of the oxidizing agents, such as hydrogen 

 peroxide and acetozone are not poisonous to man because they 

 are decomposed into relatively harmless substances before they 

 can be absorbed. Attempts to discover or to produce chemicals 

 which would exhibit a selective destructive effect upon microbes 

 in the interior of the body have not met with much success. 

 Quinine is perhaps the best known example, as it may circulate 

 in the blood in sufficient concentration to poison the malarial 

 parasites without at the same time killing the host. The effects 

 produced by mercury and by salvarsan in syphilis are perhaps 

 analogous, but they evidently depend to a large extent upon a 

 special susceptibility of the microbe, a susceptibility not yet 

 apparent in most parasites. The specific immune substances 

 may perhaps be classed in the same category. These will be 

 considered in more detail in a later chapter. 



Antiseptics. — Antiseptic and preservative agents prevent or 

 delay the development of bacteria, without killing them. Very 

 much the same agents are applied to prevent the growth of mi- 

 crobes in living tissues and consequent poisoning of the body 



