64 INFECTIOUS AND PARASITIC DISEASES. 



applied directly, or several times the quantity of boiling 

 water added to the material to be disinfected (stools, 

 for instance), and the mixture allowed to stand an hour, 

 is as trustworthy a practice as the use of any disinfec- 

 tant; and far more so than many chemicals whose 

 virtues are highly extolled in newspapers and medical 

 journals. 



We have seen that although the optimum temperature 

 for the growth of pathogenic bacteria is that of the body 

 (98.6° F.), they will multiply at a much lower tempera- 

 ture. Above the temperature of the body, however, 

 the hmit is small, since growth ceases at 109.4° F. (43° C). 

 At 140° F. (60° C.) the vegetative forms of practically 

 all bacteria are destroyed if applied for ten minutes, 

 and the time required to destroy them diminishes as 

 the temperature rises. At 212° F. (100° C.) as we have 

 stated, they are killed immediately. The tubercle 

 bacillus, although only occurring in a vegetative form 

 (i.e., does not form spores), is an exception in that 

 boiling for five minutes is required to destroy it. 



There are a large number of substances 

 Chemicals, which have a detrimental effect upon 



bacteria, some merely inhibiting their 

 growth (antiseptics), others destroying them (disinfec- 

 tants). Their number is too great to enumerate. Those 

 that interest us because they are useful in rendering 

 infectious matter harmless will be given in a later 

 chapter. 



