BACTERIA. 269 



one in each cell, and form rounded or elliptic strongly refractive 

 bodies, which appear as dark granules, and represent resting- 

 spores. These persist, while the emptied membranes of the rod- 

 lets ultimately are decomposed. In material from other cultures 

 we shall quite as commonly find rodlets which form the resting- 

 spore at one of their ends, and hence take the appearance of a pin 

 or tadpole. Many bacteria form these end-spores quite regularly, 

 while others again are characterised by swollen spindle-formed 

 spores in their centre. 



Those bacteria which form spores in the interior of their 

 cells are collected together as endosporous bacteria ; while in 

 arthrosporous bacteria entire cells take on the character of 

 spores. These latter remain, while the rest of the cells perish. 

 This conduct holds good in general for those bacteria which at the 

 time of spore-formation consist of spherical members ; while the 

 spore-forming rods and threads are especially endosporous. Endo- 

 sporous spore-formation is, indeed, essentially confined to the 

 rodlet- bacteria ; only in individual cases can it be also observed 

 in the spirally-twisted Spirillum. In very numerous bacterial 

 forms spore-formation cannot in general be found. The arthro- 

 sporously-developed spores must not be looked upon as quite 

 equivalent to those produced endosporously, but rather as only 

 a resting state of the bacteria in question. 



It is now certain that bacteria have only a very simple cycle of 

 development. The polymorphism (or pleomorphism) which was 

 formerly asserted to exist does not, as more recent researches show, 

 occur even in the most highly-differentiated sulphur and iron 

 bacteria those in which distinction between apex and base is 

 shown. 



General Reactions. In fluid substances \vhich one examines 

 for bacteria, granulations of various kinds may render observation 

 more difficult, and give rise to false impressions. We endeavour, 

 therefore, in the first place, to obtain as much information as pos- 

 sible from the fresh objects, and then, before having recourse to 

 stains, call in the aid of certain reagents. Though we can use 

 these direct, upon the fresh moist preparations, it is usually prefer- 

 able to first dry them. To effect this, spread a little of the fluid 

 uniformly upon a cover-glass, in the thinnest possible layer, by 

 means of the sterilised looped platinum wire already referred to ; 

 or upon this cover-glass thus prepared another can be laid, so that 

 the material is spread out between them, and the two separated 



