DISTINCTIVE CHARACTERS OF THE BACTERIA. 175 



by their great tendency to the formation of various 

 vegetative forms, as well as by a number of other 

 characteristics. 



The external form of a bacteric cell does not of itself afford Necessity for 

 information as to the species to which the vegetative form a copect con- 



j -i-ii -i P ception ana 



under observation belongs, but at times admits 01 various designation of 



conceptions and interpretations. If, for example, we find a an 7 given 

 spherical cell, it may be a micrococcus, a spore, or an 1%^* 

 involution product. The cell can only be designated as a 

 micrococcus when it can be proved that it arose by fission 

 from a similar spherical 'cell, and that, under suitable circum- 

 stances, it may again give rise by fission to another spherical 

 cell. For it is characteristic of the vegetative form, micro- 

 coccus, that the same spherical vegetative form repeats itself 

 through a shorter or longer series of cells. If, on the other 

 hand, the round cell has arisen not by fission but by spore 

 formation from another bacteric cell, and if it is not capable 

 of multiplying by direct fission, but must first sprout and 

 form an individual similar to the mother cell, this spherical 

 cell must be looked on as a spore. And, finally, if the 

 spherical form of the cell has arisen from a cell of another 

 shape only when it began to decay, if this spherical remnant 

 is no longer able to multiply or propagate itself in any way, 

 then we have a dead involution structure before us, to which 

 the term micrococcus cannot be applied. 



To take another example: if a twisted or spiral thread 

 comes under observation, the question arises whether it has 

 developed by fission from a cell of the same form, and 

 whether it can again give rise to a cell of a similar shape, 

 It is not till this is demonstrated that we are justified in say- 

 ing that we have to do with the vegetative form spirillum 

 or spirochoete. If this is not the case, it is possible that we 

 have before us a portion of a thread accidentally twisted, or 

 some phenomenon of decay which has arisen under abnormal 

 conditions. It is very important to be clear from the first as 

 to the meaning and the proper designation of these various 

 vegetative forms, as otherwise confusion and mistakes 

 readily occur. 



The subdivision of the four chief groups cannot be made Employment 

 exclusively according to the morphological characters ; 



the various species of bacteria which occur in the micro- f growth for 



coccal form more especially show scarcely noticeable distinction" of 



ifferences of shape under the highest powers, and even the bactena - 



the arrangement of the cocci in chains or masses pre- 



