SCHIZOMYCETES AND SACCHAROMYCETES 297 



purpose of modifying the virulence of the original virus, and 

 with more or less of success. As, for instance, a solution of 

 carbolic acid, of one part in six hundred, destroys the 

 microbes, whilst a solution of one part in nine hundred 

 attenuates the virulence without producing spores. What- 

 ever the means, the principle is the same — the reduction of 

 virulence in the bacilli, so as to produce by inoculation only 

 a mild form of the disease. 



We have now, writes Dr. Woodhead, "a whole series of 

 diseases from which immunity may be conferred by the 

 inoculation, 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 sterilised 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. Fowl- 

 cholera, certain forms of septicaemia, and a number of other 

 diseases, amongst which may be mentioned hydrophobia — in 

 which, however, the facts do not belong to quite the same 

 order — all were brought within the same zone, when it was 

 found that the introduction of the sterilised products of a 

 specific organism, first in minute doses and then in gradually 

 increasing doses, could confer a protection against the subse- 

 quent action of even the most virulent organism that, under 

 ordinary circumstances, gives rise to the same products as 

 those injected." 



The discovery of bacteria in plant diseases is more recent, 

 although B^champ noticed the presence of microzyma, or 

 bacteria, in the affected parts as long since as in 1869. Still 

 at that time, and long after, they were held to be the 

 associates, and not the cause, of disease. In 1880 Dr. Burrill 

 declared the shrivelling of pears to be due to a species of 

 bacterium, and in 1882 Wakker of Amsterdam attributed the 

 jaundice of hyacinth bulbs to the same cause. In 1885 a 

 bacterium was detected in vines said to be diseased by 

 Phylloxera, and affirmed to be the true cause of the disease. 

 More recently still, and the California vine disease 1 was 



1 Gardener's Chronicle, July 1893. 



