34 INFECTION AND IMMUNITY 



may imagine that her charm has protected it ; but 

 the evidence upon which her faith is founded is not 

 of a nature to convince those who are familiar with 

 scientific methods of demonstration. " Well edu- 

 cated " persons are often ready to testify in favour 

 of methods of disinfection or of treatment upon evid- 

 ence which, from a scientific point of view, has no 

 more value than that which the fond mother in ques- 

 tion has to offer in favour of the little bag containing 

 camphor or assafcetida or some other charm of equal 

 value which she has attached to her child's neck to 

 keep it from catching scarlet fever or diphtheria at 

 school. On a par with these charms, so far as disin- 

 fection is concerned, we may place the saucer of 

 chloride of lime, which it was formerly the fashion to 

 place under the bed of a patient sick with an infec- 

 tious disease, the rag saturated with carbolic acid or 

 chloride of zinc, suspended in the sick-room, and even 

 the fumigations with burning sulphur, as sometimes 

 practised by those who are unfamiliar with the evid- 

 ence as to the exact value of this agent and the 

 conditions necessary to insure successful disinfection 

 with it. 



Chloride of lime, sulphurous-acid gas, and carbolic 

 acid are among our most useful disinfecting agents ; 

 but disease germs cannot be charmed away by them 

 any more than by a little bag of camphor. 



