112 MICRO-ORGANISMS AND DISEASE [chap. 



that spherical globules occurring in some bacilli and being 

 in aspect and staining power comparable to young phases of 

 spores, are occasionally met with as dumb-bells within the 

 same element, but as regards the oval, bright, unmistakable 

 spores so prominent in the bacilli and their threads (bacillus 

 anthracis, bacillus subtihs, bacillus filamentosus, bacillus 

 mesentericus, &c.) it is very doubtful whether they are 

 capable of dividing or of undergoing any other change than 

 that of germination into bacilli when they are transferred to 

 new soil. 



Spores when placed under suitable conditions germinate 

 again into bacilli. This is easily observed if, for instance, 

 of any culture-material containing spores a trace is placed 

 on a cover-glass, then covered with a tiny droplet of 

 gelatine which is made rapidly to set, or in a droplet of 

 broth (" suspended drop ") and is then observed under the 

 microscope, particularly in the latter medium, which can be 

 kept on the warm stage heated to 37° C. 



Spores while fresh have a conspicuously sharp and dark 

 outline, their general aspect is glistening, and it is supposed 

 by Cohn that they are possessed of a double envelope, an 

 inner one of a fatty and an outer one of a gelatinous 

 nature : it is particularly the former which provides the 

 spores with their great resistance to drying and to heat. 

 The first indication that the spores are going to germinate 

 is shown by their outline becoming less sharp at one point. 

 This is generally at one of the poles, as in the case of 

 the spores of bacillus anthracis, bacillus filamentosus, and 

 bacillus subtilis ; or it is at one point of the long side— e.g., 

 in bacillus amylobacter, and also in the spores of some of 

 the species collectively spoken of as "potato bacillus" ; the 

 investment seems to become thinner at that point and a 

 slight pale knob appears there j this knob gradually elongates 



