VACCINATION. 375 



found that if anthrax were treated with a one half per cent, solution of 

 carbolic acid, it became distinctly attenuated. Chamberland and Roux 

 found that fresh cultures started from one that had been subjected for 

 twelve days to .16 per cent, solution of carbolic acid were fatal to 

 guinea-pigs and rabbits, whilst if the time during which the bacillus was 

 exposed to this solution of the acid was extended to twenty-nine days and 

 a cultivation then made, such cultivation was no longer capable of killing 

 a rabbit. They were thus able to produce a virus of any degree of attenua- 

 tion and to preserve it for some time, as the cultures made from their 

 attenuated bacilli inherited the same degree of attenuation that had been 

 developed by the bacilli that had actually been treated with the acid. They 

 found that bichromate of potash and other antiseptics exerted a similar 

 attenuating influence. It has also been shown that the passage of the 

 anthrax bacillus through a series of animals of a certain species will 

 render the anthrax bacillus more or less virulent, according to the 

 species that is used. Thus Klein found that blood taken from a white 

 mouse which had died of anthrax was a protective vaccine for sheep, 

 whilst Sanderson and Duguid observed that the virus obtained from a 

 guinea-pig dead of anthrax was modified so far as cattle were concerned. 

 Roy made a series of similar observations. It must be borne in mind, 

 however, that cattle very frequently recover from anthrax under ordinary 

 treatment, so that these latter observations can, as yet, scarcely be accepted 

 as fully proved. 



Up to this time it had not been recognized that the 

 immunity was really conferred by the action of the soluble 

 products of the organism. Pasteur had indeed shown that 

 the general symptoms of fowl cholera could be induced by 

 the inoculation of the sterilized products of the fowl 

 cholera germ, and Chauveau had suggested that an 

 acquired immunity was due to the action of the soluble 

 products of the microbe. He argued from an observation 

 that, although in pregnant sheep, anthrax bacilli with 

 which they had been inoculated were unable to pass into the 

 foetus, the lambs exhibited an extraordinary immunity 

 against attacks of anthrax, this immunity, he considered, 

 being necessarily the result of the action of the soluble 

 products that had been able to pass over from the maternal 

 to the foetal circulation. We have now a whole series of 

 diseases from which immunity may be conferred by the inocu- 

 lation or introduction into the tissues of an animal of the 

 soluble products of pure cultures of micro-organisms. 

 In America, hog cholera has been vaccinated against, the 

 vaccinator using the sterilized cultures of the hog cholera 

 organism as his protective virus. Wooldridge, who was the 

 first to adopt this principle in connection with anthrax, was 

 followed by Pasteur and Perdrix, and by Hankin, whose 



