220 INFECTIOUS AND PARASITIC DISEASES. 



resistance to heat. Such vegetative forms of bacteria as 

 are more resistant to heat, are more resistant to chem- 

 icals ; and the sporulating forms are even more difhcult 

 to kill with chemicals than with steam under pressure. 

 Chemical disinfectants vary greatly in the strength of 

 each required to be efficient, and their disinfecting 

 powers also vary with the material to be disinfected. 

 Very powerful disinfectants may fail to act on account 

 of chemical union taking place between them and the 

 material in which the infectious agents are contained. 

 Thus both bichloride of mercury and carbolic acid 

 lose much of their disinfecting qualities when added to 

 albuminous material, on account of the formation of an 

 insoluble albuminate which is inert. Furthermore, if 

 one of these substances be used in excess in the belief 

 that the above defect may be overcome, the end is 

 just as likely not to be realized, because this insoluble 

 combination surrounds the infectious agents and pre- 

 vents contact between them and the disinfectants. 

 In instances of this kind either the chloride of lime, the 

 cresols, or formalin are to be preferred. Where the 

 medium contains much organic matter or filth, even 

 where the proper disinfectant is used, much stronger 

 solutions than commonly employed are advisable. An 

 extremely valuable point to remember in applying any 

 of the chemical disinfectants is that the disinfecting 

 power of all of them is greatly enhanced if they are 

 heated with the material to be disinfected; and the 



