1 8 BIOLOGICAL LECTURES. 



French Academy of Sciences of July 12, 1880, entitled 

 " Immunity from Anthrax (' charbon ') Acquired as a Result 

 of Protective Inoculations." 



In this paper he announces his discovery of the important 

 fact that the anthrax bacillus does not form spores in the tis- 

 sues or liquids of the body of an infected animal, but multiplies 

 alone by binary division, " sa multiplication se fait toujours 

 par une division du mycelium." 



In the same communication he reports his success in con- 

 ferring immunity upon five sheep by means of protective 

 inoculations, and also upon four young dogs. We must, there- 

 fore, accord him the priority in the publication of experimental 

 data demonstrating the practicability of accomplishing this 

 result. 



But it is especially to the experimental researches of Pasteur 

 that we are indebted for the development of practical methods, 

 which have been extensively employed in protecting cattle, 

 sheep, and swine from the fatal effects of various infectious 

 maladies, and man from hydrophobia as the result of the bite 

 of a rabid animal. 



Pasteur's inoculations are made with an "attenuated virus," 

 i.e. with a culture of a pathogenic micro-organism which has 

 a diminished degree of virulence and which when introduced 

 into a susceptible animal induces a non-fatal and comparatively 

 mild attack. 



The researches of Pasteur and of his followers in this line of 

 investigation show that pathogenic virulence may be attenuated 

 by prolonged exposure to oxygen ; by exposure to a tempera- 

 ture a little below that which would completely destroy vitality; 

 by the action of certain chemical agents ; and in some cases, 

 by passing through a series of non-susceptible animals. 



As a general rule pathogenic virulence is increased by suc- 

 cessive inoculations in susceptible animals and diminished by 

 cultivating the pathogenic micro-organism in artificial media 

 outside of the animal body or by passing it through animals 

 having but slight susceptibility to its pathogenic action. As 

 pathogenic virulence depends, to a considerable extent at least, 

 upon the formation of toxic substances during the active 



