102 MICRO-ORGANISMS AND DISEASE. [CHAP. 



elementary mass of protoplasm, or it may be only in a small 

 number. In the first case : a consecutive series of spores is 

 present in the bacilli, two spores if the bacillus is composed 

 of two elementary cells, four in a chain of four elementary 

 cells, or a vast number in a leptothrix. In the second case : 

 a bacillus composed of two or four elementary cells may 

 contain only one spore at one end or in the middle, or one 

 at each end, or two together in the middle ; in the leptothrix 

 spores are seen only at comparatively long intervals. The 

 position of the spore in the bacillus is generally so that the 

 long axis of the spore is parallel to that of the bacillus ; but 

 exceptionally it may be placed obliquely or even transversely. 

 The bacilli in which spore-formation has set in are always 

 much thicker, twice or more, than those in which no spore- 

 formation has occurred ; and as has been stated above, the 

 sheath swells up and remains for some time as a hyaline 

 gelatinous capsule around the spore, but sooner or later this 

 is also lost and the spore becomes quite free. When spore- 

 formation has taken place in a convolution or in a mass of 

 leptothrix, and after the sheaths of the bacilli have become 

 swollen up into a gelatinous matrix, it looks as if we had a 

 zooglcea, in which the bright oval spores form the particular 

 elements embedded in a more or less hyaline gelatinous 

 matrix. But even in these cases on careful analysis it is 

 noticed that the spores have a linear or serial arrangement, 

 being originally developed in filaments. 



This spore-formation occurs in many species of bacilli, and 

 it closes the cycle of the life-history of the bacilli. But it 

 does not take place under all circumstances. In the case of 

 many bacilli, e.g. hay-bacillus, anthrax-bacillus, bacillus of 

 putrefaction, spore-formation occurs only when there is an 

 ample supply of oxygen, e.g. when the bacilli grow on the 

 surface of the nourishing material (Cohn, Koch). It has 



