I.] THE HISTORY OF THE COMMA-BACILLUS. 15 



but in the latter case they would die off, and there would be 

 no necessity for disinfecting. I am inclined to hold the 

 latter view, as borne out by all the experience I have so 

 far had. 



" In these cultivation-experiments it was further seen that 

 the nutritive substances at least, the gelatine and meat- 

 broth must not be acid. As soon as the gelatine shows 

 only a trace of acid reaction, the growth of the comma- 

 bacilli is very stunted. If the reaction be in a marked 

 degree acid, the development of the bacilli completely 

 ceases. It is at the same time noteworthy that it is not 

 all acids that seem to be unfavourable to the comma- 

 bacillus ; for the surface of a boiled potato, where it is 

 cut, is known to have an acid reaction, in consequence, if, 

 I am not mistaken, of its containing malic acid. Never- 

 theless, comma-bacilli grow very luxuriantly on potatoes. 

 Hence, one cannot say, straight off, that all acids hinder 

 the growth ; but, in any case, there are a number of acids 

 which have this effect. In meat-broth it is probably lactic 

 acid, or an acid phosphate. 



" In these experiments on the influence of substances in 

 arresting the development of comma-bacilli, the striking fact 

 was evident that comma-bacilli die off extremely easily when 

 dried. These experiments were made by letting a very 

 small drop of a substance containing bacilli dry on a cover- 

 glass, and a large supply of these cover-glasses was immedi- 

 ately prepared for a series of experiments. A drop of the 

 liquid which was to be examined was then placed upon 

 such a cover-glass, and left for development in the hollow 

 glass slide. Having proceeded in this manner, in no single 

 preparation did anything grow that had received meat-broth 

 as nutritive fluid, nor in a striking manner in the test- 

 preparations either. At first I did not know what caused 



