4 SCIENCE PROGRESS. 



sonous albumoses, while Sydney Martin proved that specific 

 albumoses and alkaloids are produced in the animal body 

 by the multiplication of the bacilli. Kitasato studied the 

 tetanus toxin, and found that it is of a specific nature. 



A further important contribution was made by showing 

 that by repeated injections of small non-fatal doses of pure 

 toxin, or of larger doses of weakened toxin (the effect of 

 weakening being caused by the addition of various chemical 

 substances or by heating), an otherwise susceptible animal 

 may be furnished with gradually increasing resistance, not 

 only against fatal doses of toxin but of the bacilli them- 

 selves. That a high degree of resistance or tolerance 

 amounting in some cases to immunity can be produced in 

 otherwise susceptible animals by the injection of attenuated 

 living; bacilli dates back to the researches of Pasteur on 

 protective inoculations against anthrax and against fowl 

 cholera, and this principle has been applied to various other 

 infectious diseases by many subsequent observers. Now, 

 with regard to tetanus and diphtheria, the observations of 

 Behring and Kitasato, Fraenkel and Brieger, Roux 

 and others have established that by injecting animals 

 repeatedly with gradually increasing amounts of either 

 attenuated culture, or with (non-fatal) small doses of pure 

 toxin, or with larger doses of weakened toxin — produced by 

 the microbe of tetanus or diphtheria respectively in artificial 

 culture — a high state of tolerance can be ultimately achieved 

 whereby these animals become possessed of immunity. 

 And it appears as a further result of these observations, 

 particularly those of Behring and Kitasato, Roux and 

 Vaillard, Roux, ( i) that the amount of attenuated culture or of 

 toxin required for each injection stands in indirect proportion 

 to the initial susceptibility of the animal experimented upon, 

 and (2) that the degree of resistance thus acquired is con- 

 siderable in tetanus and soon reached, while in diphtheria it 

 is reached only slowly, after a large number of preliminary 

 injections, and is at no time of the nature of absolute 

 immunity, though its degree increases as the injections 

 increase in amount and number. Thus, for instance, in 

 Roux's experiments, it is shown that a horse, even after it 



