POWERS OF RESISTANCE. 411 



and have been found alive after being exposed for several 

 hours to the temperature of -10 C. They are, however, 

 killed by being kept in ice for a few days. Against the 

 ordinary antiseptics they have comparatively low powers of 

 resistance, and Pfuhl found that the addition of lime, in the 

 proportion of i per cent, to water containing the cholera 

 organisms, was sufficient to kill them in the course of an 

 hour. 



As regards the powers of resistance in ordinary con- 

 ditions, the following facts may be stated. In cholera 

 stools kept at the ordinary room temperature, the cholera 

 organisms are rapidly outgrown by putrefactive bacteria, but 

 in some cases they have been found alive even after two or 

 three months. In most experiments, however, attempts to 

 cultivate them even after a much shorter time have failed. 

 The general conclusion may be drawn from the work of 

 various observers that the spirilla do not multiply freely in 

 ordinary sewage water, whilst they may remain alive for a 

 considerable period of time. In distilled water they remain 

 alive for several weeks at least, but do not multiply, nor 

 does any considerable growth take place without the 

 presence of a pretty large proportion of organic matter. 

 On moist linen, as Koch showed, they can flourish very 

 rapidly. When the cholera organisms are grown along with 

 other organisms in fluids at a warm temperature, it is found 

 that at first they may multiply more rapidly than the others, 

 but that after a certain time they are outgrown by some 

 of the organisms present, gradually diminish in number, and 

 ultimately disappear. It must not, however, be inferred 

 from such experiments that a similar result will necessarily 

 follow in nature, as any particular saprophytic organism 

 requires a special habitat that is, certain suitable con- 

 ditions for its growth in competition with other organisms. 

 Though we can state generally that the conditions favour- 

 able for the growth of the cholera spirillum are, a warm 

 temperature, moisture, a good supply of oxygen, and a con- 

 siderable proportion of organic material, we do not know 

 the exact circumstances under which it can flourish for an 



