12 THE BIOLOGY OF BACTERIA 



environment are favourable. The capsule of a large, or "mother" 

 cell, shows a slight protrusion outwards, which is gradually -enlarged 

 into a " daughter " yeast, and later on becomes constricted at the neck. 

 Eventually it separates as an individual. The protoplasm of the 

 spores of yeasts differs, as Hansen has pointed out, according to the 

 conditions of culture. 



Division, or fission, is the commonest method of reproduction. 

 It occurs transversely. A small indentation occurs in the capsule, 

 which appears to make its way slowly through the whole body of the 

 bacillus or micrococcus until the two parts are separate, and each 

 contained in its own capsule. It has been pointed out already that 

 in the incomplete division of micrococci we observe a stage precisely 

 similar to a diplococcus. So also in the division of bacilli an appear- 

 ance occurs described as a diplobacillus. 



Simple fission requires but a short period of time to be complete. 

 Hence multiplication is very rapid, for within half an hour a new 

 adult individual can be produced. It has been estimated that at this 

 rate one bacillus will in twenty-four hours produce millions of similar 

 individuals; or, expressed otherwise, Cohn calculated that in three 

 days, under favourable circumstances, the rate of increase would be 

 such as to form a mass of living organisms weighing many tons, and 

 numbering billions of individuals. Favourable conditions do not 

 occur, fortunately, to allow of such increase, which, it is evident, can 

 only be roughly estimated. But the above facts illustrate the 

 enormous fertility of micro-organic life. When we remember that in 

 some species it requires 10,000 or 15,000 fully-grown bacilli placed 

 end to end to stretch the length of an inch, we see also how exceed- 

 ingly minute are the individuals composing these unseen hosts. 



Spore formation may result in the production of germinating cells 

 inside the capsule of the bacillus, endospores, or as modified individuals, 

 arthrospores. The body of a bacillus, in which sporulation is about 

 to occur, loses its homogeneous character and becomes granular, owing 

 to the appearance of globules in the protoplasm. In the course of 

 three or four hours the globule enlarges to fill the diameter of the 

 rod, and assumes a more concentrated condition than the parent cell. 

 At its maturity, and before its rupture of the bacillary capsule, a 

 spore is observed to be bright and shining, oval and regular in shape, 

 with concentrated contents, and frequently causing a local expansion 

 of the bacillus. In a number of rods lying endwise, these local 

 swellings produce a beaded or varicose appearance, even simulating 

 a streptococcus. In the meantime the rod itself has become slightly 

 broader and pale. Eventually it breaks down by segmentation or 

 by swelling up into a gelatinous mass. The spore now escapes and 

 commences its individual existence. Under favourable circumstances 

 it will germinate. The tough capsule gives way at one point, 



