SPOKE FORMATION 7 



other conditions of life being equal). The presence of substances 

 excreted by the bacteria themselves plays, however, a more 

 important part in making the surroundings unfavourable than 

 the mere exhaustion of the food supply. A living spore will 

 always develop into a vegetative form if placed in a fresh food 

 supply. With regard to the rapid formation of spores when 

 the conditions are favourable for vegetative growth, it must be 

 borne in mind that in such circumstances the conditions may 

 really very quickly become unfavourable for a continuance of 

 growth, since not only will the food supply around the growing 

 bacteria be rapidly exhausted, but the excretion of effete and 

 inimical matters will be all the more rapid. 



We must note that the usually applied tests of a body 

 developed within a bacterium being a spore are (1) its staining 

 reaction, namely, resistance to ordinary staining fluids, but 

 capacity of being stained by the special methods devised for 

 the purpose (vide p. 102) ; (2) the fact that the bacterium 

 containing the spore has higher powers of resistance against 

 inimical conditions than a vegetative form. It is important to 

 bear these tests in mind, as in some of the smaller bacteria 

 especially, it is very difficult to say whether they spore or not. 

 There may appear in such organisms small unstained spots the 

 significance of which it is very difficult to determine. 



The Question of Arthrosporo.us Bacteria. It is stated by Hueppe that 

 among certain organisms, e.g. some streptococci, certain individuals may, 

 without endogenous sporulation, take on a resting stage. These become 

 swollen, stain well with ordinary stains, and they are stated to have 

 higher power of resistance than the other forms ; further, when vegetative 

 life again occurs it is from them that multiplication is said to take place. 

 From the fact that there is no new formation within the protoplasm, 

 but that it is the whole of the latter which participates in the change, 

 these individuals have been called arthrospores. The existence of such 

 special individuals amongst the lower bacteria is extremely problematical. 

 They have no distinct capsule, and they present no special staining 

 reactions, nor any microscopic features by which they can be certainly 

 recognised, while their alleged increased powers of resistance are very 

 doubtful. All the phenomena noted can be explained by the undoubted 

 fact that in an ordinary growth there is very great variation among the 

 individual organisms in their powers of resistance to external conditions. 



Motility. As has been stated, many bacteria are motile. 

 Motility can be studied by means of hanging-drop preparations 

 (vide p. 63). The movements are of a darting, rolling, or 

 vibratile character. The degree of motility depends on the 

 species, the temperature, the age of the growth, and on the 

 medium in which the bacteria are growing. Sometimes the 

 movements are most active just after the cell has multiplied, 



