260 TEXT-BOOK OF BACTERIOLOGY. 



The micro-organism of cholera asiatica belongs, by its morpho- 

 logical peculiarities, to the class of spiral bacteria, and is hence 

 consistently called, by strict systematicians, Vibrio or Spirillum 

 choleras asiaticae. Its true form appears, indeed, very distinctly 

 as a short, rather clumsy rod, about half as long as the tubercle 

 bacillus, but considerably thicker, with round ends and a more or 

 less pronounced curve along its longitudinal axis. The degree of 

 the curvature varies from almost straight cells to nearty semi- 

 circular ones. It corresponds closely in appearance to the comma of 

 certain faces of type, for which reason Koch gave this bacterium 

 the name of " Comma bacillus/' by which it has attained general 

 celebrity and which we shall retain on account of its historical sig- 

 nificance. 



It must, therefore, be borne in mind that the expression " bacil- 

 lus " is, in reality, not correct. Whenever a bacterium prepares to 

 form groups, it will become evident that it is not a "bacillus." If 

 we had a simple curved rod only, it would have to form a more or 

 less complete circle if it continued to grow long enough. But genu- 

 ine, neatly turned screws, long spirilla, arise which sometimes attain 

 a very considerable length. Even a single individual must possess, 

 besides the curve, a distinct twist, a torsion, and sometimes by the 

 use of good lenses we are able to see the beginning of a screw, 

 namely, a single comma bacillus. Hence the rods are to be looked 

 upon as only fragments of a real spirillum. 



In examining cholera preparations the developed spirilla are not, 

 in fact, frequently met with. They seem to arise only under special 

 circumstances, usually only when the development (the rapid, 

 continual transverse division and increase) is in some way disturbed 

 and impeded. In hanging drops, for instance, the screws are very 

 numerous. If the bacteria live under unfavorable conditions, e.g., if 

 either the temperature is unsuitable or if the nourishing solution 

 contains small quantities of alcohol, tincture of opium, etc., thus 

 scarcely permitting their growth, such conditions favor the appear- 

 ance of spirilla, which are evidence that the regular division of the 

 cells has been retarded, thereby causing the formation of groups. 



The comma bacillus appears, as a rule, singly or in pairs (as 

 stated above); in the latter case they grow end to end, the curves 

 facing in different directions, resembling the letter S. 



The cholera bacteria possess an extremely lively motion, pro- 

 viding they are cultivated at a suitable temperature and receive 

 proper nourishment. They crowd and whirl through the micro- 

 scopic field " like a swarm of dancing gnats." The spirilla, too, pos- 

 sess the same faculty : they glide along with short and swift un- 



