BACTERIA. 53 



true ramification, like that of the mould-fungi, does not occur 

 in bacteria. Eods and filaments frequently assume wavy or 

 spiral forms (h) ; when they are only slightly curved, we have 

 the vibrio form ; when the spirals are more prominent, the 

 spirillum, and spirochcete forms ; when they intertwine like 

 a plait of hair, the form called spirulina is produced. To 

 these must be added the remarkable irregular, swollen, or 

 curved forms which many bacteria can assume ; the cause of 

 this alteration is, however, not sufficiently known involution 

 forms (i\ 



We will now select one of these forms and submit it to a 

 thorough examination with a magnifying power of about 

 1 ,000 diameters. Like every other cell, it contains protoplasm, 

 a homogeneous, feebly refractive mass, in which infinitesimal 

 particles can be detected here and there, especially if the 

 cell is not in its most active growth. Sometimes a bright 

 spot is found in the middle of the cell, which, from analogy 

 to the higher plants, is considered to be a sap-cavity or 

 vacuole. In some bacteria certain solid substances have been 

 detected, as, for instance, sulphur grains in bacteria which live 

 in water containing sulphur ; in some species the plasma can, 

 under certain conditions, be coloured blue by iodine, which 

 indicates the presence of substances resembling starch. 



Surrounding this protoplasmic body we find a cell-wall 

 or membrane. An examination of this by means of staining 

 will generally show that this membrane in its outer layers is 

 swollen up into a gelatinous mass, which becomes especially 

 distinct when masses of bacteria are aggregated together. 

 From a chemical standpoint it must be provisionally assumed 

 that this cell-wall is of a different nature in different species. 

 In some it reminds us of the cellulose of the higher plants, 

 whilst in others it appears rather to resemble the albuminoids 

 in its properties. 



Many bacteria contain blue, red, yellow, or green colouring 

 matters, which sometimes cause very intense coloration. 

 Under the microscope, however, the individual bacteria 



