PHYSICAL DISINFECTING AGENTS 257 



is known to produce spores is lockjaw; for while there are 

 some other disease germs which do produce spores, the ordi- 

 nary diseases of the household which we look upon as con- 

 tagious are not, so far as we know to-day, disseminated 

 by means of spores. Hence the practical conclusion is 

 that for all of the common household diseases a moist tem- 

 perature of 150 or 1 60, maintained for half an hour, 

 is sufficient for disinfection ; but it must always be 

 borne in mind that this will not disinfect spore-producing 

 material. 



Sunlight. Bacteria cannot stand direct sunlight for more 

 than a few hours without being killed, the brighter 

 the light the more efficacious its action. While sunlight 

 is thus an acceptable germicide, its practical value is 

 limited because it has little power of penetration. Thin 

 materials, like sheets, which can be exposed to direct sun- 

 light, will be disinfected in the course of a few hours, but 

 heavier materials, like blankets, will be disinfected only 

 on their surface. Anything on which the sunlight can 

 shine directly may easily be disinfected by this means, 

 but in dimly lighted rooms light is of little value as a 

 disinfectant. Its use is therefore limited to such articles 

 as can be removed from the rooms and exposed to the 

 sun's rays. 



Cold. Cold is almost useless as a disinfectant. It 

 delays the growth of bacteria for a while, but does not 

 destroy them. We have already seen that long-continued 

 freezing in ice will, after some months, destroy typhoid 

 bacilli, but, except in the case of a few diseases, like 

 yellow fever, freezing is of no value as a -disinfecting 

 agent. 



