ESSAYS ON BACTERIOLOGY. 25 



the- chemical germicides are poisons. Their use there- 

 fore to the point of destruction of the bacteria might 

 also result in destruction of the host. Obstetricians 

 have learned this by some bitter experiences. It is 

 therefore a matter of very practical value to know that 

 below the point of lethal strength these agents may 

 prevent, or so far retard the growth of bacteria as to 

 make their action truly disinfectant. It is well to re- 

 member this, that it is not an irrational nor a useless 

 thing to use weak solutions of disinfectants. 



Another point which has been made clear is, that 

 the relative practical A'alue of these agents is not the 

 same as their relative germicidal power, and that the 

 strongest germicide is not necessarily always the best 

 to use. This fact rests not solely upon the poisonous 

 quality of some of the chemical disinfectants, but 

 upon other grounds also. Thus, the bi-chloride of 

 mercury, in the presence of albumen, is thrown down 

 as an insoluble albumenate. This everyone has seen 

 in dressing a bleeding wound. Solutions of this sub- 

 stance, even when made with ordinary distilled water 

 of the shops, may be much weaker than their users 

 innocently believe. Hence, the plan of adding such 

 agents as ammonium chloride or tartaric acid to pre- 

 vent this change. Other things of minor importance 

 are also to be taken into account in deciding the ques- 

 tion of the practical utility of germicides, as their irri- 

 tant, corrosive, or staining properties, their cost, odor, 

 solubility, etc. 



