110 EFFECT OF CHEMICALS ON BACTERIA 



point. By means of this highly sensitive test as little as one-billionth 

 part of a milligram of oxygen may be detected. 



It is quite possible that the phagocytes which play such a part 

 in freeing the body of bacteria are directed or guided in their choice 

 and perception by chemotaxis to the bodies which they ingest. 

 The attraction of leukocytes toward the point of bacterial invasion 

 is, in part at least, due to the properties of the bacterial proteins. 

 This attraction is sometimes increased by injecting into the tissues 

 at the point of infection some bland substance, such for instance as 

 bismuth subnitrate. 



Disinfectants. Of great interest are those substances which in 

 minute quantities destroy the life of the cell. These substances 

 when considered in their effects upon man and animals are called 

 poisons. But when considered from the standpoint of micro- 

 organisms they are called germicides. Analogous with the general 

 term germicide, are the terms bactericide and fungicide. A disin- 

 fectant is a substance which destroys the causative agent of infec- 

 tion. Although disinfection may occasionally mean sterilization, in 

 the majority of cases it does not. It implies the destruction of those 

 minute forms of life which cause disease. 



Antiseptics prevent decomposition and decay. They do not 

 necessarily destroy microorganisms; they prevent their growth and 

 activity. One and the same substance may be a disinfectant under 

 one condition and an antiseptic under another. Formalin in the 

 proportion of 1 to 50,000 is an antiseptic, whereas it requires from 

 3 to 10 per cent, solution to be a disinfectant in a reasonably short 

 time. Mercuric bichlorid in the proportion of 1 to 300,000 will 

 sometimes prevent the germination of anthrax spores. Yet it 

 requires a 1 to 1000 solution to kill them. 



The term preservative is usually applied to those substances 

 which are added to foods, feeding-stuff, and substances of similar 

 origin with the intention of preventing decomposition or decay. 

 These may be either comparatively poisonous benzoic acid, boric 

 acid, salicylic acid, formalin, or sulphates or the non-poisonous 

 substances common salt or sugar. The method of action of the 

 two is markedly different, the first combining with the protoplasm 

 of the cell, the second acting through increased osmotic pressure. 



Deodorants are substances which have the power of destroying 

 or masking unpleasant odors arising from putrifying or fermenting 

 organic matter. Deodorants destroy odors, disinfectants destroy 

 germs. A deodorant may or may not be a disinfectant. Formalin 

 is a good disinfectant and deodorant, whereas charcoal is a good 

 deodorant but has no value as a disinfectant. 



The classification of disinfectants is difficult, inasmuch as we do 

 not understand in many cases their complete mode of action. 

 Moreover, almost any compound, if used in sufficient concentration, 

 may act as an antiseptic if not as a disinfectant. The methods 



