REPRODUCTION BY SPORULATION 15 



threatened with extinction from adverse circumstances. 

 Each spore consists of a little mass of protoplasm enclosed 

 within a very tough and resisting membrane, which tends 

 to preserve its vitality even under unfavourable condi- 

 tions ; for spores resist the action of desiccation and 

 germicidal agents to a much greater degree than the 

 fully developed organisms. Endospores vary much in 

 size and in the position they occupy within the bacterial 

 cell in the different species ; their diameter is usually 

 about the same as that of the cell in which they are 

 developed, but may be much greater, and in position 

 they may be central or terminal, and sometimes the 

 spore-bearing cells are swollen or club-shaped ; these are 

 termed " clostridia." Endospores are still unknown in 

 a large number of species. The other variety of sporula- 

 tion, arthrospore formation, is of doubtful occurrence, 

 but is stated to take place as follows : Some of the ele- 

 ments formed by fission are slightly larger, more refractile, 

 and more resisting than their fellows, and are stated to 

 have the properties of spores. 



Placed in favourable circumstances, the spore in either 

 case germinates, it beomes swollen and granular, and 

 loses its refractile appearance ; a slight protuberance 

 forms, this increases in size, and an organism similar 

 to the parent one is finally reproduced ; frequently the 

 empty spore membrane at first encloses one extremity, 

 and is afterwards cast off. In certain instances the 

 spore germinates without casting its membrane, the 

 spore membrane becoming the cell- wall of the young 

 organism. The ellipsoidal spores of the B. anthracis 

 sprout from the end, those of B. subtilis from the 

 side (" polar " and " equatorial " germination respec- 

 tively). 



On the Morphology, etc., of the Bacteria see Dobell, Quart. 

 Journ. Micr. Sci., vol. 56, 1911, p. 395 (Bibliog.) ; Penau, Comp. 



