32 PRINCIPLES OF BACTERIOLOGY 



in length, and thus coccus-like forms result; but when these are given 

 fresh food under suitable conditions they elongate and reproduce 

 the usual shaped organisms. According to recent investigations on 

 the subject of cell reproduction, the division of the cell starts from the 

 protoplasmic layer, the central space being passively destroyed, and the 

 outer envelope is only secondarily concerned in the process. This would 

 indicate that the central space is not a true nucleus, otherwise the 

 division of the nucleus should precede the cell division. The complete 

 process of cell reproduction in most varieties occupies, under favorable 

 conditions, about twenty to thirty minutes. 



But although elongation in the greater diameter and transverse 

 division is the rule for the majority of bacteria, there are certain groups, 

 as the sarcinse, for example, which divide more or less regularly in 

 three directions. Instead of becoming separated from each other as 

 single cells, the tendency then is for the segmentation to be incomplete, 

 the cells remaining together in masses. The indentations upon these 

 masses or cubes, which indicate the point of incomplete fission, give to 

 these bundles of cells the appearance commonly ascribed to them 

 that of a bale of rags. As already said, division in two opposite direc- 

 tions results in the formation of a group of forms as tetrads. Division 

 irregularly in all directions results in the production of clusters. The 

 rod-shaped bacteria never divide longitudinally. 



REPRODUCTION AMONG THE HIGHER BACTERIA. Most of the higher 

 bacteria consist of thread-like structures more or less septate and often 

 surrounded by a sheath. The organism is frequently attached at one 

 end to some object or to another individual. It grows to a certain length, 

 and then at the free end certain cells called gonidia are cast off, from 

 which new individuals are formed. The gonidia do not possess any 

 special powers of resistance. 



Spore formation must be distinguished from vegetative reproduction. 

 This is the process by which the organisms are enabled to enter a stage 

 in which they resist deleterious influences to a much higher degree than 

 is possible for them in the growing or vegetative condition. It is true 

 that in all cultures a certain proportion of the bacteria are more resistant 

 than the average. No difference in protoplasm, however, has been 

 noted in them. They are probably the youngest and most hardy or 

 perhaps involution forms. The difference between these and the less 

 resistant forms is not great. Some have believed that this resistance was 

 due to certain bodies called arthrospores, or jointed spores, developed 

 not within the cell, but as a sprout-like separation of one of its extremi- 

 ties. Recent researches into the formation of arthrospores have 

 resulted in questioning their existence. There is, therefore, in the lower 

 bacteria, only one kind of spores requiring special notice viz., endo- 

 spores. These are strongly refractile and glistening in appearance, 

 oval or round in shape, and composed of concentrated protoplasm 

 developed within the cell (Figs. 17 and 18). They are characterized 

 by the power of resisting the injurious influences of heat, desiccation, 

 and chemical disinfectants. 



