458 THIRD PART.—BACTERIA OR SCHIZOMYCETES. 
‘a. Regard being had solely to the shape of the isolated cells or to 
their simplest genetic union, — 
1. Cocci: isolated cells which are isodiametric or at least very slightly elongated 
in one direction. These are distinguished. when necessary according to their 
dimensions into mzcrococct, macrococct and monad-forms. 
2. Rod-like forms: cells elongated in one direction and cylindrical, rarely 
fusiform, isolated or in a short chain. These again are distinguished into 
short rods (Bacteria), long rods (Bactili), fusiform rods (Clostridia) and some others. 
3. Spiral forms: spirally twisted rods, some with narrrow coils (Spirillum, 
Sptrochaete), some with distant and very steep coils (Vibriones). 
It follows necessarily from what has been already stated that no sharp line of 
distinction as regards their shape can be drawn between short rods, for instance, arid 
cocci, or between a slightly twisted Vibrio and a Bacillus which departs to a trifling 
extent only from a mathematically straight line; nor can they at present be always 
clearly distinguished by their structure. . 
This is especially the case with respect to the rod-like forms, since a rod may be 
a single cell of the corresponding shape, or a number of cells firmly connected together 
and closely related to one another genetically. In the latter case while the cell is 
dividing repeatedly, the partition-wall may be of so delicate a structure that the com: 
pound body, if not carefully examined, may be taken for a simple homogeneous 
body. Hence when these organisims are simply spoken of as rods we must under- 
stand that the writer is alluding to their outward appearance only, unless the structure 
also is exactly described. 
To these three kinds must be added a fourth, namely the swollen bladder-like 
forms. Individuals of this kind are found in company with the other three and are 
evidently produced from them ; they are distinguished by having their cell swollen to 
several times the size of the other form, with a knobbed and irregular outline, 
These inflated forms have been observed in artificial cultivations where the nutrient 
substances are in insufficient quantity or are exhausted; Zopf and Cienkowski found 
them in Cladothrix and Crenothrix, Buchner and Prazmowski in forms of Bacillus, 
and Neelsen in Bacterium cyanogenum. They are therefore considered to be 
diseased states of the other forms, and have been termed by Nägeli and Buchner 
involuiton-forms. Hansen, on the other hand, has shown that they occur very 
frequently, indeed almost invariably, with the Bacteria of mother of vinegar; we do 
not know whether they have not some further meaning in this and perhaps also in 
most other cases. 
6. According to the mode of the connection between the individual 
cells, each of the above form-groups may be,— 
I. free, that is not firmly joined together, though occurring in the society of 
great numbers of like individuals. 
2. in the form of filaments, that is joined together and forming long filiform 
rows. These filaments are unbranched in most Schizomycetes and then the form is 
known as Lepfothrix or Mycothrix ; they are branched in a few cases only (Cladothrix). 
In the latter form one extremity of a cell bends outward from the row in which 
it occurs, and continues its growth and divisions in a divergent direction. The 
