172 BACTERIA. 



the dead cholera patient, but in those to whom has fallen the 

 duty, a day or two later, of washing the soiled linen used by the 

 patient during life. In the first case the attendant is exposed 

 to the action of the bacillus as it comes from the patient, but 

 at a time, it is argued, during which the organisms are more 

 readily destroyed, either in the dejecta, or by drying ; but the 

 attendant who has to wash the soiled linen may be attacked 

 by the bacillus after it has had time and opportunity to 

 develop on the damp sheets, in the presence of air, and when 

 it has acquired a greater power of resistance, and has become 

 much more dangerous. It has now, in fact, lost its anaerobic 

 habit, and has become adapted to its new surroundings, with 

 the result that it is much more resistant and is better qualified 

 to live outside the body and to resist the action of ordinary 

 germicidal reagents, or of the acid gastric juice, should it find 

 its way into the stomach of a fresh host. 



In similar fashion may be explained the fact that when 

 the drying zone becomes limited, the cholera bacillus appears 

 to die out more readily. It appears that the micro-organism 

 passing directly from the faeces into very damp soil contain- 

 ing insufficient oxygen to satisfy its saprophytic requirements 

 is, on account of its feeble resisting powers, "suffocated" at once, 

 or within a very short period. Where, however, the depth of 

 the drying zone increases, there is more air (oxygen) in the soil, 

 the organisms are more able to multiply in its presence, and, 

 taking the field against other putrefactive organisms, gradually 

 become more and more hardy, acquire the aerobic and sapro- 

 phytic habit, and thus become more dangerous to the inhabi- 

 tants of the locality in which all this occurs. It must be re- 

 membered, however, that the term "drying zone" is entirely a 

 relative one, and that it may still contain, as it usually does, 

 sufficient moisture for the wants of the cholera organism. That 

 the organism takes some little time to pass from the aerobic to 

 an anaerobic condition is evident from Koch's early experi- 

 ments, in which he made plate cultivations of cholera bacillus, 

 and then, before the gelatine was perfectly set, covered about 

 one-third of the surface with exceedingly thin glass cover 

 glass thickness or split mica. He then found that colonies 

 grew as usual, and became visible to the unassisted eye in the 

 uncovered portion of the gelatine and for a very short distance 

 under the covering plate (2 mm.). He observed, however, 

 that where the air (oxygen) was cut off, the colonies did not 



