MICRO-ORGANISMS IN RELATION TO MAN, 103 
cholera spreads from its home in Lower Bengal to surrounding 
districts and distant countries. At first such spread was 
thought to be most erratic and inexplicable; now, however, 
there can be little doubt that it follows a very definite line of 
advance in the various epidemics, and travels along the ordin- 
ary lines of commerce by railways, caravans, and ships, from 
the regions in which it is endemic to those centres of trade and 
religion, which, by their imperfect sanitary arrangements, by 
the want of cleanliness of their inhabitants, by meteorological 
conditions, and by reason of their bad water supplies, are 
ready for its reception and propagation. 
As you will readily believe, the possibility of micro-organ- 
isms playing a part in the propagation of cholera had not been 
neglected, but it was not until Dr. Koch—being sent by the 
German Government to Egypt and India to study the disease 
in its home—was able to demonstrate a peculiar species of 
bacterium as the causal agent, that any definite proof of the 
micro-organismal nature of the contagium of the disease could 
be obtained. Koch’s conclusions met with much opposition, 
and Dr. Klein, one of our leading bacteriologists, took a very 
active part in that opposition in England; judging, however, 
from the reports from his laboratory which appeared during 
the recent epidemic, he has now adopted Koch’s views, and 
the latter’s ‘“‘comma” bacillus must be regarded as the causa 
causans of the disease. 
The comma bacillus usually occurs as a slightly curved rod, 
measuring from one to two twenty-five-thousandths of an inch 
in length, the average length being one seventeenth-thousandth 
of an inch; it is about one fifty-thousandth of an inch in thick- 
ness, the average thickness being about one-third to one-fourth 
of the length. Instead of occurring as single rods, these 
organisms may be grouped in pairs, or even in larger num- 
bers, in which case the curve may be continuous or reversed, 
thus giving rise to the formation either of half-circles or of 
S-shaped curves. In cultivations in meat-broth the bacilli 
