382 APPLIED BACTERIOLOGY 



much more effective than when used by itself, though salt 

 has practically no disinfectant capacity. The action, how- 

 ever, of a disinfectant may be impeded by other substances 

 in which it is conveyed. For instance, the presence of 

 soap, which in itself possesses some disinfectant capacity, is 

 liable to impede the action of mercuric perchloride ; and 

 most ointments, with the exception of those in which 

 ' lanolin ' forms the base, reduce the disinfectant action of 

 most substances which may be conveyed in them. 



For certain purposes disinfection has been attempted by 

 the use of solid substances, such as powders, possessing 

 very slight solubility, or by inert solids steeped in dis- 

 infectant solution and dried. It is obviously a condition 

 of disinfectant action that the substances should come in 

 contact with every organism; and when the size of the 

 organism is considered, it will be seen that the difficulties 

 of disinfection are considerably increased by dispensing 

 with the liquid form. In practice it is safe to say that 

 nothing more than deodorant and mildly antiseptic effect 

 can be obtained from such substances. The chief danger 

 to which they give rise is, that persons who are sufficiently 

 credulous to use them are liable to regard them as justify- 

 ing neglect of those more effective precautions of cleanliness 

 and of true disinfection which are of real service. 



Many vapours have a well-marked disinfectant action. 

 It, may, however, be stated broadly that, until some means 

 of Obtaining an equal diffusion of a vapour in atmospheric 

 air can be provided, the use of disinfectant in the form of 

 vapour or gas must be largely illusory. A considerable 

 number of experiments have been made demonstrating the 

 action of vapours in glass bells and under laboratory con- 

 ditions; but such observations avoid the difficulty of 

 diffusion of vapours and gases in general into air to a much 

 larger extent than is possible in practice. 



