CHOLERA. 153 



The * comma ' bacillus, which is now regarded as belong- 

 ing to the spirilla, usually occurs as a slightly curved rod, 

 measuring from I to 2/* in length, with an average length 

 of about 1.5/1 ; it is .5 to .6/* in thickness, the average 

 thickness being about one-third to one-fourth of the length. 

 It is therefore from one-half to one-third the length of 

 the tubercle bacillus, but somewhat thicker. In place of 

 occurring as single rods these organisms may be grouped 



Photo-micrograph cholera bacilli, x 1000. Long spirilla, comma, S and O shaped 

 organisms. Some involution forms. 



in pairs, or in larger numbers, in which case the curve may 

 be continuous or reversed, so giving rise to the formation 

 either of half circles or of S-shaped curves. In cultivations 

 in meat broth the bacilli may be so grouped that they form 

 long wavy or spiral threads, each of which may be made up 

 of 10, 20, or even 30 short turns. 



Such are the characters of the organisms which Koch found, 



