242 SCIENCE FROM AN EASY CHAIR 



The circumstances which determine whether the 

 cholera-bacillus, when it gets into the human intestine, 

 will develop and cause an attack of cholera, or will simply 

 be digested or will remain alive, but inactive, for a time, 

 have yet to be exactly determined. Obviously a knowledge 

 of them must be of immense importance. Certain experi- 

 ments show that other minute parasitic organisms 

 especially those called Sarcina (Fig. 46, e\ which often, but 

 by no means always, are abundant in the human intestine 

 favour the growth of the cholera-bacillus in fact, prepare 

 the ground or soil, as we may call it, for that deadly 

 organism. This has been shown experimentally by 

 sowing cholera-bacillus on plates of slightly acid gelatine, 

 or jelly. It will not grow on this, but if at certain points 

 on the surface of the jelly the Sarcina organism is planted, 

 then it is found that all around the points where the 

 Sarcina is growing the cholera-bacillus also flourishes and 

 multiplies. And it seems probable that, just as there are 

 microbes which are adjuvant or helpful to the cholera 

 microbe, so there are others which are repressive or 

 destructive of it. We know that this is the case with 

 regard to some other microbes namely, that a microbe 

 which will flourish abundantly on a prepared jelly if it is 

 alone, is entirely repressed and arrested in its growth by 

 the presence of one other ascertained kind. It is, in fact, 

 thus that some of the commoner putrefactive kinds of 

 microbes occurring in river water are repressive of the 

 typhoid-bacillus, which, if it should get there, flourishes 

 best in the purest water or in water containing no other 

 microbe. There is some ground for thinking that in 

 certain districts there may be microbes present which 

 make their way into the human intestine, and then 

 actually repress the cholera-bacillus, should it subsequently 

 be taken in with food or water. It would, of course, be 

 of immense importance to discover such a microbe, if it 



