248 SCIENCE PROGRESS. 



produce an anthrax virus so modified by heat that it 

 would not form spores, after which by treating the micro- 

 organism as he had already treated the fowl cholera bacillus 

 he was able to obtain an attenuated virus which was capable 

 of setting up a modified attack of the disease, and so of 

 protecting the vaccinated animal against the attack of the 

 more virulent microbe. His successful and striking" experi- 

 ments at Melun have been so often quoted that it is un- 

 necessary to go into them again, but it may be well to point 

 out that out of this work has arisen our knowledge that 

 vaccination against anthrax, and against certain other 

 diseases, can protect most efficiently in most cases, and 

 for a considerable length of time ; but it is evident that 

 there are cases in which, either through the extreme 

 susceptibility of the patient, or the intense activity of the 

 infecting virus, only partial protection is obtained, whilst 

 even in the most perfectly protected individual the effect of 

 vaccination passes off after a time and leaves the patient 

 again comparatively vulnerable to attack. 



Having reduced the virulence of the fowl cholera and 

 anthrax organisms, the next step was to see if their virulence 

 could be restored. In the case of the bacillus anthracis this 

 was done by passing the attenuated form through a very 

 young guinea-pig, which, it was found, succumbed to the 

 disease even when inoculated with the weak vaccine; a drop 

 of blood from this animal inoculated into one a little older 

 causes its death, and so on until the blood taken from an 

 aged animal which has succumbed to the inoculation anthrax 

 suffices to kill sheep, and that from the sheep, an ox. This 

 method of exaltation of the virulence of a virus has since 

 then been used with great effect in the production of active 

 toxins necessary for the production of antitoxins, now so 

 much spoken of. Before leaving this part of our subject, it 

 may be well to point out that it was in connection with the 

 fowl cholera group of organisms that Pasteur was enabled 

 to show that the products of the micro-organisms, from 

 which the micro-organisms themselves had been removed, 

 were capable of setting up many of the symptoms of disease, 

 that they had in fact active toxic or poisonous properties. 



