LIFE HISTORY OF BACILLUS ANTHRACIS. 163 



The division into two or more pieces is not always a very 

 rapid process. A rod (Plate XI, fig. 20) which was watched 

 till it divided was at first made up of three pieces, and one 

 of them from the beginning looked as if it might at any 

 moment detach itself from the others ; but after six hours' 

 almost constant struggling, though by that time able to 

 remove itself half its own length from the other two seg- 

 ments, it was still connected by a very delicate thread, and 

 before separation, which took place after being under 

 observation for over seven hours, it in a comparatively short 

 time was almost divided into two segments, so that when it did 

 escape from the other apparently inactive pieces it wriggled 

 about the field like two freely movable links of a chain. 



After assuming this motile phase for some time the rods 

 lengthened out into spore-bearing filaments (Plate XI, fig. 

 22). A mouse inoculated with the spores thus obtained died 

 forty-eight hours after, presenting all the usual appearances 

 of splenic fever, and thus proving that the motile rods were 

 none other than a hitherto undescrihed phase of Bacillus 

 ajithracis. 



What the conditions are which lead to these movements 

 remain to be discovered. Apparently the same conditions 

 do not always lead to the same results, for several generations 

 may elapse before the motile phase again appears. 



The lengthening of the rods into filaments is an extremely 

 rapid process, and is apparently effected by the temperature. 

 In five hours a rod, at a temperature of 32° C. may have in- 

 creased so as to be from eighty to one hundred times its 

 original length, and in twenty-four hours the filament may 

 be full of spores. If the temperature, however, is kept 

 about 28° C, the spores may not appear till the thirty-sixth 

 or fortieth hour. When the spores have once appeared all 

 the other changes go on at ordinary temperatures, from 12*^ 

 to 18*^ C, but not nearly so rapidly, even when the prepara- 

 tion is kept in the sun for a few hours daily, as when artifi- 

 cial heat is applied. On the other hand, a high temperature, 

 37° — 40° C, at once checks all developmental changes. 



The filaments differ very much in their arrangement. 

 Sometimes they form a network — indeed a mycelium — 

 made up of bundles of numerous, nearly parallel, unbranched 

 threads, crossing each other at different levels ; the threads 

 are sometimes straight but have generally a wavy outline. 

 This condition may obtain throughout the whole prepara- 

 tion, but generally at some parts the filaments are extremely 

 irregular and much convoluted. In some cultivations all 

 the filaments may be so irregular that they may best be 



