CHAP.X. MORPHOLOGY OF THE BACTERIA. ENDOSPOROUS BACTERIA. 461 



cylindrical sister-cells, is attached to the spore as a longer or shorter appendage. 

 Such structures with one swollen sporiferous extremity are the ' capitate Bacteria ' 

 of older writers. In other species there is less difference in size between the spore 

 and the mother-cell, though the latter is never quite filled by the spore. In 

 Spirillum amyliferum and Bacillus (Clostridium) butyricus, which show the granulose- 

 reaction before the formation of the spore, the spot where the comparatively small 

 spore begins and completes its formation is, according to Van Tieghem, a terminal 

 portion of the mother-cell in which there is no granulose. 



The motile forms may continue their movement during the development of the 

 spore ; they become stationary as l;he spore matures, and finally in all cases the 

 membrane of the mother-cell dissolves sooner or later and the spore is set at 

 liberty. 



In most of the species which have been examined the formation of spores 

 coincides with the moment when the substratum has expended its nutrient material 

 or from other causes, such as an accumulation of products of fermentation, has 

 become unfitted to support the vegetation of the species. At the same time the 

 phenomenon does not always depend on the quality of the substratum. Prazmowski 

 has shown that Bacillus butyricus may be in active process of vegetative multiplication 

 while some of its cells are forming and maturing their spores. 



The formation of spores when once begun extends usually to the greater 

 number of the isolated cells and aggregates of cells in a pure culture; but a 

 certain number of the cells remain sterile, and no definite rule determining their 

 distribution has yet been discovered. The parts which remain sterile are seen to 

 break up and disappear if fresh nutriment is not supplied in time ; if it is supplied 

 they may continue to vegetate. Plants grown in quantity in a pure medium and 

 left to themselves often produce enormous masses of ripe spores. 



The ripe spore varies from round to elongate-ellipsoidal or cylindrical according 

 to the species. It has the appearance, as has been already said, of a highly 

 refringent usually colourless body (reddish in Bacillus erythrosporus, Cohn) with a 

 dark and sharply defined outline; in some cases it looks like an oil-drop, but 

 reagents show that the resemblance to the latter is only superficial. It consists of a 

 highly refrirtgent mass of protoplasm, which with our present means of investigation 

 is perfectly homogeneous. This protoplasmic body, as is shown in germination, 

 is closely surrounded by a thin but firm and often apparently brittle membrane; 

 outside the cell-wall may often be seen a pale slightly refringent envelope with 

 lightly marked contour and of apparently gelatinous consistence, the material com- 

 position of which cannot be exactly ascertained, but which forms a delicate covering 

 to the spore, and sometimes also appears to be prolonged at each extremity of the 

 spore into a small tail-like appendage. Pasteur 1 was the first who described these 

 appearances but he did not distinctly recognise their significance. 



The bodies in question are proved by their germination to be spores. They 

 are in a condition to germinate, as soon as they have reached the development 

 described above at the expense of the mother-cell; and they retain the power of 



1 Etudes sur la maladie des vers a soie, I, 228. 



