BY C. J. POUND, F.R.M.S. Xlll 



•organisms have been In-onght to light, it is a remarkable fact that 

 this discovery of Koch still holds the same unique position, for 

 not a single new bacillus has been found with the characteristic 

 square-cut ends of the Anthrax bacillus. 



IMMUNITY AND PROTECTIVE INOCULATION. 



During his investigations Pasteur discovered that cattle and 

 sheep, after recovering from one attack of Anthrax, were pro- 

 tected from a second attack, and in 1882 he elaborated a method 

 by which a mild form of the disease could be given to animals, 

 which rendered them perfectly harmless against a subsequent 

 inoculation with virulent bacilli. He found that the continued 

 growth of Anthrax bacilli at an aluiormally high temperature 

 (42 to 43 degrees Centigrade) caused them to lose their power of 

 developing endospores, and also to gradually lose their virulence. 

 In fact this virulence can be gradually attenuated till it ceases to 

 be dangerous even to that most susceptible of all experimental 

 animals, the domestic mouse. Prompted l)y the result of these 

 discoveries, Pasteur then attempted with success to use the 

 attenuated bacillus of Anthrax for protective inoculation agai)ist 

 the virulent bacillus. He was able to show that if an animal is 

 inoculated with the l)acillus attenuated to the degree recpiisite 

 for it — that is, for that species of animal — it either does not 

 sicken, or it sickens slightly and recovers from the disease. 

 It resists then the infection with less attenuated bacilli, and 

 after the next inoculation it resists the bacilli which possesses the 

 highest degree of virulence. Pasteui- did not delay in making 

 this brilliant laboratory achievement aAailal)le for practical 

 application. The hrst great experiment with this attenuated 

 virus outside the laboratory is particularly noteworthy, ami of 

 such historical interest tbat 1 cannot refrain from giving a l)rii4' 

 account of it. 



On the 5th of ^lay, IKHl, Pasteur obtained 24 sheep, 1 go;it, 

 and C) cows (all of which are peculiarly susceptible to Anthrax), 

 and inoculated them with the fully attenuated virus, and 12 days 

 later they were again inoc\ilated with a rathe.i less attenuated, 

 oi' rather stronger virus. On the ;$lst of ]Mav all these inoculated 

 a.nimals, as well as 24 sliec'i), 1 goat, and 4 cows not pi'e\i()iisly 

 inoculated, received sevei'ally an injection of viruU^it blood tVom 



