186 BACTERIA. 



the pellicle which formed on the surface at the end of five 

 days, sterilized it in an autoclave at 120° C, and then injected 

 from two to six c.c. of the fluid expressed from the sterilized 

 mass into the muscles of a guinea pig, the animal was rapidly 

 and completely protected against the action of Koch's comma 

 bacillus, introduced in the ordinary fashion. By further 

 experiments he found that by simply keeping for several days 

 the sterilized mass in which the dead bacilli still remained 

 a much larger quantity of the poison could be obtained — 

 sufficient, in fact, to kill the animal when given in the same 

 dose as before, but still protecting the animal when exhibited 

 in smaller doses. (Here the organisms could no longer be 

 producing the poison, but it appears as though there was 

 stored up in their body a considerable quantity which could 

 only diffuse out into the fluid after a certain lapse of time.) 

 To Gamaleia also we owe the knowledge that this 

 organism may become very much modified in various ways, 

 and some of the experiments he carried out provide us with 

 an explanation of some of the most important facts connected 

 with the increase and decrease in virulence of type, in cases 

 that occur during the " rise and fall " of an epidemic. 



He was able to increase the virulence of the special comma bacillus in a most 

 remarkable manner. After obtaining a growth of the organism in broth he 

 introduced a small quantity of the culture into the lung of a white rat ; this 

 was followed by an acute form of croupus pneumonia accompanied by 

 marked pleurisy, the animal rapidly succumbing. With the fluid that ac- 

 cumulated in the chest a second animal was inoculated in a similar fashion, 

 with the result that this animal died more rapidly than the first. This 

 inoculation was continued through a whole series of animals, until finally 

 the rats succumbed very rapidly indeed, and an organism was found not in 

 the intestine, but in very large numbers in the blood.' 



In addition to drying, acid, and the other destructive 

 reagents already mentioned, it has been found that a very 

 considerable number of chemical reagents arrest or prevent 

 the growth of the cholera bacillus. 



Koch's list contains alcohol, 10 per cent., sulphate of iron, 2 per cent, 

 (this latter acts first as an acid, and secondly as a precipitant of the 



' That this may have a bearing on Wood's observations as to the viru- 

 lence of the organism in the serobic and anaerobic conditions is most evident, 

 and is well worth further investigation. 



