CHAP. X.—MORPHOLOGY OF THE BACTERIA.—ENDOSPOROUS BACTERIA, 461 
cylindrical sister-cells, is attached. to the spore as a longer or -shofter 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 the 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 2 
highly refringent 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 proloriged at each extremity of the 
spore into a small tail-like appendage. Pasteur? 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. 
