CHAP.X. — MORPHOLOGY OF THE BACTERIA. — ENDOSPOROUS BACTERIA. 465 



spore in a cell is indicated by the apppearance of a small roundish highly refringent 

 body in the protoplasm, usually close to the surface of one extremity of the cell. The 

 nature of this body cannot be clearly made out, but the first impression which it 

 conveys is the same as if one of the highly refringent bodies just mentioned as 

 disseminated through the protoplasm had increased somewhat in size. The body 

 then grows perceptibly larger while the protoplasm round it diminishes (Fig. 194 

 d, e,f). In the course of a few hours it grows into a longish cylindrical object, which 

 is shown by its subsequent behaviour to be a spore. The spore is slightly shorter than 

 the cell which produces it, but its breadth is only from a third to one half of it. It 

 has a sharply defined outline, appears to be perfectly homogeneous, is very highly re- 

 fringent, and has a bluish tint. This is the appearance which it presents long before it 

 attains to its full size. As it grows, the protoplasm which surrounds it becomes con- 

 tinually clearer and more transparent ; when full-grown it lies straight or oblique in a 

 pellucid substance within the membrane of the mother-cell, which is persistent for a 

 time, but which if kept in the fluid at length disappears entirely and leaves the spore at 

 liberty. Only one spore is ever formed in each cell. It is remarkable how often the 

 formation of spores begins in the terminal cells of a rod, though this is not always the 

 case, and proceeds rapidly from them to the adjacent cells. It takes place not 

 unfrequently in all the cells of a rod, and always in the majority of them in 

 successful cultures ; but single cells often prove an exception to this rule, and spores 

 sometimes begin to form in a cell but are never fully developed. In all these cases 

 the cells which do not produce spores die off unless a timely supply of fresh nutriment 

 excites some of them to renewed vegetation. 



The movement of the rods becomes slower perhaps when spores begin to be 

 formed, but does not at once cease, and this is highly inconvenient for those who are 

 watching the process of spore-formation. It is only when all the cells of a rod have 

 formed spores, or those which produce no spores are dead, that the rods lose the 

 power of motion. 



The germination of the spores (Fig. 194 g-ni) has been observed in material 

 kept dry for at least 24 hours after maturation. If material in this state is placed in 

 a fresh nutrient solution, the cells in which no spores have formed cease to grow, and 

 drop off one by one. The membranes of some of the sporiferous cells may have burst 

 before desiccation, otherwise they still remain round the ripe spore; in the latter 

 case they are now seen to swell up gradually and dissolve, so that the spores are 

 released from the previous combination. At the same time the dark outline and the 

 high refringent power of the spore itself disappear, and it assumes the uniformly pale 

 aspect of a rod when actively vegetating, having its outline, especially at the 

 extremities, at most only a little more distinctly defined than in the rest of its 

 body. In this condition it increases slowly in volume during several hours (8-12 

 in the observed cultures) till it has become as broad as a normal rod without 

 essentially deviating from its original shape. Then not unfrequently a thin 

 membrane divides transversely or obliquely into two portions and is all at 

 once separated from its surface, and the delicately circumscribed cell slips out, 

 having the breadth, shape and structure of a short rod, and then grows rapidly 

 in the direction of its previous longer axis and commences the active vegetation 

 described above. 



f 4 ] H h 



