GENERAL PRINCIPLES. 183 



by such organisms, distinct in form and equally distinct 

 in functions, each variety of which produces a train of 

 symptoms peculiar to itself. Some of these are powerless 

 to affect certain species of animals or individuals. It is 

 now definitely known that the greatest scourges that afflict 

 man and his dumb companions are attributable to these or 

 to similar lowly-organized animal forms. 



And it might be well to point out that most of the 

 recent advances in human medicine, especially in that most 

 important department of preventive medicine, have been 

 owing to experiments on the domestic animals, or on ani- 

 mals living about human habitations. 



These minute organisms, by feeding on the fluids and 

 tissues of the animal, cause as they are present in vast 

 numbers, mechanically, and more especially by direct irri- 

 tation, and by the poisons they produce an effect on the 

 entire organism that may be best termed poisoning ; and, 

 of course, the greater the vigor of the animal, the better 

 prepared it is to withstand such influences and to eliminate 

 both the micro-organisms themselves and their poisons. 

 As yet our knowledge of combating these enemies is con- 

 fined to preventive inoculation in the case of a few dis- 

 eases all that can be desired, perhaps, if it were established 

 for all microbic maladies and to preventing infection in 

 some degree. But direct destruction of the germs when 

 once within the body remains as one of the triumphs to be 

 attained. Nevertheless, it can not be denied that the 

 progress of medicine within the past decade has never 

 before been in the slightest degree approached. 



