MODE OF MULTIPLICATION 65 



in pairs (Fig. 2, c); tetrads — those developing as fours (Fig. 

 2, d); and sarcince — those dividing into fours, eights, etc., 

 as cubes — that is, in contradistinction to all other forms, the 

 segmentation, which is rarely complete, takes place regularly 

 in three directions of space, so that when growing the bundle 

 of segmenting cells presents somewhat the appearance of a 

 bale of cotton (Fig. 2, e). 



To the bacilli belong all straight, oval and rod-shaped 

 bacteria — i. e., those in which one daimeter is always greater 

 than the other. In this group are found those organisms the 

 life-cycle of many of which presents deviations from the 

 simple rod shape. Many of them in the course of development 

 increase in length into long threads, along which traces of 

 segmentation may usually be found. Again, under certain 

 conditions, many of them possess the property of forming 

 within the body of the rods oval, glistening spores (see Fig. 6), 

 and, if the conditions are not altered, the rods may entirely 

 disappear and nothing be left in the culture but these oval 

 spores. In some of them this phenomenon of spore-formation 

 is accompanied by an enlargement or swelling of the bacillus 

 at the point at which the spore is located (see Fig. 6, c and d). 

 Again, many of them, from unfavorable conditions of nutri- 

 tion, aeration, or temperature, undergo pathological changes 

 that are probably autolytic in nature — that is, the indivi- 

 duals themselves experience degeneration of their proto- 

 plasm with coincident distortion of their outline; they are 

 then usually referred to as "involution-forms" (see Fig. 5, 

 a and b). In all of these conditions, however, so long as 

 death has not occurred, it is possible to cause these forms 

 to revert to the typical rods from which they originated, 

 by the renewal of conditions favorable to their normal 

 vegetation. 

 5 



