18 APPLIED BACTERIOLOGY 



viduals, or even families, being poisoned by partaking of 

 some particular meat, fish, or other food, that has had the 

 opportunity of undergoing partial decomposition. These 

 cases are invariably due to the fact of the food in question 

 being in an unsound condition, whereby it contained or- 

 ganisms which generated the poison ; and even though the 

 bacteria may have been destroyed during the process of 

 cooking, the toxic substance remains in the food, to produce 

 the most disastrous effects on its being eaten. 



These pathogenic organisms, which under ordinary cir- 

 cumstances cause disease and death, can by proper methods 

 be so modified in their properties that they can be made to 

 serve as antidotes to the very diseases they cause. This 

 discovery, which was due to the genius of Pasteur, is the 

 greatest romance of modern science ; it has opened a new 

 epoch in the annals of medicine, and has revolutionized the 

 treatment of disease. 



Taking only one case for example : The bacillus of 

 anthrax, if cultivated at a temperature rather higher than 

 blood-heat, becomes no longer fatal when inoculated into 

 animals, but produces only a slight constitutional disturb- 

 ance, after which treatment the animals are found to be 

 ' immune,' or protected against the virulent form of 

 anthrax. This great principle of an ' attenuated ' virus 

 conferring immunity is the basis of many systems of pro- 

 tective treatments which are becoming of ever-increasing 

 importance in the conflict with infectious disease. A full 

 account of the theory and practice of these ' antitoxin ' treat- 

 ments will be found later. 



Eesistancb of the Bactebia to External Influences. 



Bacteria, like other living organisms, are exposed to many 

 outside influences. These we will consider under six heads, 

 namely, Light, Heat, Cold, Desiccation, Electricity, Chemical 



