ix ] BACILLUS. 69 



sinks to the bottom of the fluid ; after another day or two a 

 new pellicle is formed, and so on until the material is 

 exhausted. 



Any part of this pellicle examined .under the microscope 

 shows itself to be a zoogloea in the true sense of the word, vast 

 numbers of shorter or longer bacilli crossing and interlacing 

 and lying embedded in a gelatinous hyaline matrix. As with 

 bacterium termo, one occasionally notices at the margin of the 

 mass one or other bacillus wriggling itself free and darting 

 away. And in the case of non-motile bacilli, putrefactive and 

 others, I have also seen distinct formations of zooglo3a, having 

 the shape of spherical or oval lumps of various sizes composed 

 of a hyaline jelly-like matrix, in which are embedded the 

 bacilli in active multiplication. 



In those species in which the bacilli jire capable of forming 

 leptothrix (leptothrix buccalis, hay-bacillus, anthrax-bacillus) 

 the filaments may form dense convolutions. When in these 

 convoluted filaments spores are formed (see below) and the 

 sheaths of the filaments swell up and become agglutinated into 

 a hyaline jelly-like substance, the spores appear to form a sort 

 of zoogloea. 



Bacilli are killed by drying, but it is necessary to bear in 

 mind that they must be exposed to the drying process in thin 

 layers (Koch). At the temperature of boiling water they are 

 invariably killed, but not their spores. Even heating them 

 from half an hour to several hours at a temperature above 55 

 or 60 C. kills them. Freezing also kills them, but not their 

 spores. Carbolic acid, corrosive sublimate, thymol, &c., kill 

 them. 



One of the most striking phenomena in the growth of bacilli 

 is their power of forming spores. These are generally oval 

 when fully developed, spherical when immature ; they are 

 always of a bright glistening appearance, and take dyes either 

 with difficulty or not at all ; they are generally a little thicker 

 than the bacilli within which they have developed. Their 

 formation always takes place in this way : in one or other 

 elementary cubical, spherical, or rod-like mass of protoplasm 

 there appears a bright dot ; this enlarges at the expense of the 

 protoplasm until in its fully developed state it has an oval 

 shape. The whole of the protoplasm of an element is not 

 consumed in this process, a small trace always remaining unused 

 at one or both ends. The sheath enlarges, and the bacillus 

 looks much thickened ; then the sheath breaks, and the spore 

 with the remnant of protoplasm becomes free. Soon this 

 remnant disappears, if it had not disappeared while the spore 



