400 BACTERIOLOGY. 



toms and pathological tissue changes that are seen to 

 occur in the course of infection by the organisms them- 

 selves. 



In some instances the production of the poisonous 

 principles, even under artificial conditions of cultiva- 

 tion, is of a most astonishing nature, and poisons result 

 that, in the degree of their toxicity, exceed anything 

 hitherto known to us. For instance, the potencies 

 of the poisons that have been isolated from cultures of 

 the badllas diphtherioe and the bacillus of tetanus have 

 been carefully determined by experiments upon animals, 

 and it has been found that 0.4 milligramme of the 

 former is capable of killing eight guinea-pigs, each 

 weighing 400 grammes, or two rabbits, each weighing 

 three kilogrammes (Roux and Yersin ') ; and that 0.0001 

 milligramme of the latter will produce tetanus in a 

 mouse, with all the characteristic manifestations of the 

 disease (Brieger and Cohn^). 



In short, infection may be best conceived as a contest 

 between the invading organisms on the one side and the 

 resisting tissues of the animal body on the other, the 

 weapons of offense of the former being the poisonous 

 products of their growth, and the means of defense 

 possessed by the latter being substances which are, so 

 to speak, antidotal to these poisons. If the tissue ele- 

 ments are not of sufficient vigor to neutralize the bac- 

 terial poisons, the bacteria are victorious, and infection 

 results, while, if there is failure to establish a condi- 

 tion of disease, the tissues are victorious, and are said to 

 be resistant or to possess immunity to this particular 

 form of infection. 



1 Annales de I'Institut Pastear, tome iii., 1889, p. 287. 



2 Zeitschr. filr Hygiene u. Infektionskrankheiteu, Bd. xv., Heft i., 1893. 



