22 MICRO-ORGANISMS AS PARASITES. 



proved utterly erroneous and misleading." Suffice it to say that 

 Koch went out to Egypt and to India, that he examined nearly a 

 hundred specimens of choleraic infection, and likewise examined, 

 with the minutest care, cases of typhoid and typhus fever, 

 dysentery, and intestinal catarrli. In all the former cases the 

 comma bacilli were present ; in all the latter they were absent, 

 although i\\e post-?/iorte/n appearances in typhus resembled those 

 of cholera in a marked degree. Koch, therefore, came to the 

 conclusion that the bacillus found in cases of cholera, and of 

 cholera alone, were the exciting cause of that disease, hitherto 

 supposed to be due to an " organic poison," which had a 

 preference for living in the earth. (See Quain, " Dictionary of 

 Medicine.") 



Nothing could be more strange than the way in which the 

 merest novices in microscopical work rushed into print to say 

 that Koch was mistaken. An experienced biologist would weigh 

 his evidence anxiously before venturing to break a lance with one 

 of the greatest scientists on his own ground, but as the homely 

 proverb says, "Fools rush in where angels fear to tread." Dabblers 

 with the microscope found a comma-shaped bacillus in the mouths 

 of healthy persons, and rushed to the medical journals to announce 

 the discovery, and to say that Koch's comma bacillus could be 

 found everywhere and every day. Had they merely read his 

 paper once, and remembered what they had read, they would 

 have known that one bacillus being often much like another, its 

 life-history must be patiently studied before its identity can be 

 proved. The comma bacillus of cholera, sown in a flask of 

 gelatine, behaves in a manner peculiar to itself. As the colony 

 of bacilli grow, they liquify the gelatine on which they rest, and 

 sink further down into it, causing "^fuiind-sliaped depression. 



Nothing can be stranger than to read the peculiarities of 

 constitution of each kind of micro-organism, when its life-history 

 is studied. The comma bacilli prefer a temperature of from 30*^ 

 to 40° C, but they are not extremely particular in this respect. They 

 "do quite well," as Koch says, at a temperature of 17° C., though 

 under 16° C. their growth stops altogether. They bear freezing 

 perfectly well. As food they enjoy strong soups, nourishing 

 jellies, and milk; in weak broth they do not thrive at all. Though 



