BACTERIOLOGY. 63 



growing side by side with pathogenies, the latter get 

 less food and suffer from the excretory products of the 

 former. Hence in the process of putrefaction, as of 

 sewage or of diseased carcasses, self- purification is 

 largely brought about by the saprophytes crowding out 

 the weaker pathogenies. 



Another natural force tending to the 

 Bactericidal destruction of bacterial life is the hacteri- 

 PowER OF cidal^ action of the body-juices of all 

 Body-juices, living things. The number of bacteria 



which rest upon our bodies, and even get 

 into the interior, is incalculable, yet very few do us 

 harm on account of this property of living matter. 

 This protective power of the body when displayed 

 against a disease is called immunity. 



The destructive action of heat upon bac- 

 Heat. teria is so well known that it often comes as 



a surprise that, in disinfection, more con- 

 fidence should be placed in chemicals. As a matter of 

 fact, there is no more efficient disinfectant than heat 

 if properly applied. It is also the cheapest. With few 

 exceptions, bacteria are killed in a few minutes at a 

 temperature considerably below the boiling point of 

 water; and at the boiling point at once. Yet it is a 

 common practice for both physicians and nurses to put 

 a family to considerable expense for chemical disinfec- 

 tants in a case of typhoid fever, for example, when heat 

 ♦Bacteria destroying. 



