30 BACTERIOLOGY. 



sisting of a number of individual cells strung together 

 like beads or pearls upon a string ; diploeocei — those 

 growing in pairs; tetrads — those developing as fours, 

 and sarcince — those dividing into fours, eights, etc., as 

 cubes — that is, in contra-distinction to all other forms, 

 the segmentation, which is rarely complete, takes place 

 iu three directions of space, so that when growing, the 

 bundle of segmenting cells presents somewhat the ap- 

 pearance of a bale of cottou. 



To the bacilli belong all rod-shaped organisms, i. e., 

 those in which one diameter is always greater than the 

 other. 



In this group are found those organisms the life cycle 

 of many of which present deviations from the simple 

 rod shape. Many of them in the course of developmeut 

 increase in length into long threads along the course of 

 which traces of segmentation may usually be found — 

 the anthrax bacillus and bacillus subtilis are conspicuous 

 examples of this. Again others, under certain condi- 

 tions, possess the property of forming within the body 

 of the rods oval, glistening spores, aud if the conditions 

 are not altered the rods may entirely disappear, so that 

 nothing may be left in the culture but these oval forms. 

 Again, many of them, from unfavorable conditions of 

 nutrition, aeration, or temperature undergo pathological 

 changes — that is, the individuals themselves experience 

 alterations in their protoplasm which result in distor- 

 tion of their outline. This is the production of the 

 so-called " involution forms." But in all of these con- 

 ditions, so long as death has not actually occurred, it is 

 possible under favorable conditions to cause these forms 

 to revert to the original rod-shaped bacilli from which 

 they originated, 



