DISTINCTIVE CHARACTERS OF THE BACTERIA. 173 



they are at all capable of development they again grow 



into hacilli under favourable conditions, either directly 



or after an intermediate stage. The bacilli occur either 



in a quiescent stage, in which case they are often 



arranged in threads, heaps or zooglsea, or in a swarm- 



ing stage. In many forms, however, the latter stage 



has not yet been observed. Now and then a mis- 



take may be made between rods and micrococci when 



the rods are in an upright position and present their 



circular transverse section to the observer's eye ; a 



correct conclusion may usually be arrived at by care- 



ful examination with repeated alteration of the fine 



adjustment of the microscope, and by comparison with 



neighbouring individuals. It is at times uncertain Distinction 



whether an elongated cell constricted in the middle is mlcTococci 



a diplococcus or a rod. The sharp, acute-angled con- bacimortLro 



striction which is noticeable after the division of a which arc un- 



coccus, and the round form of the two halves, may serve dhXk^ or 



as a means of distinction when contrasted with the those which 



Ur6 pleLCOCl HL 



less acute constriction of the rod, and the fact that the right angles 



,.,.,,, i> . T-I i to the field of 



single individuals are never isodiametric. Even here, vision. 

 however, it is only after comparison with other reigh- 

 bouring cells, or after continued observation of the 

 further development of the individual cell, that an 

 absolute conclusion can be arrived at. Young br c'lli, 

 which have just been formed by fission, or by the 

 sprouting of a spore, often show a very slight excess of 

 one diameter over the other, and thus approach the 

 vegetative form, micrococcus, but are easily distin- 

 guished from it by their further development, and 

 by the presence at the same time of older forms. 

 Finally, in the spore form a confusion between bacilli Distinction 

 and micrococci could also occur, if it were not 

 that the higher refracting power of the spores, and the 

 feeble manner in which they take up aniline colouring 

 matters, formed good points for their recognition ; the 

 diagnosis is rendered certain by the study of the further 

 behaviour of the two cells, the sprouting of the one to 

 form a bacillus, and the multiplication of the other by 

 division to form fresh spherical colls. 



