§ X.] Bacterium Termo. Parasitic Bacteria. 107 



extraordinary large quantities. Isolation by cultivation in gela- 

 tine is not possible, because the gelatine is at once liquefied by 

 the rapid multiplication of the Bacteria. 



Microscopic examination reveals a number of minute rod-like 

 cells, according to Cohn's measurement about 1-5 ft in length, 

 and becoming one-half or one-third of that amount in breadth, 

 engaged in active bipartition, and thus frequently united in pairs, 

 but scarcely ever forming long rows; in this they resemble Micro- 

 coccus lacticus, but are distinguished from it by their somewhat 

 larger dimensions, and especially by the very active independent 

 movement of the individuals suspended in the fluid. The move- 

 ment is often a peculiar backward movement in different direc- 

 tions. Zoogloeae are ultimately formed on the surface of 

 the fluid in the form of greenish slimy films or lumps, in 

 which the cells lie motionless. The alternation of these two 

 states was clearly described by Cohn as long ago as 1853. 

 Formation of spores in the characteristic manner has not been 

 observed in B. Termo, and it must therefore be classed for the 

 present with arthrosporous forms. I have said thus much in 

 order to commend the old B. Termo to renewed observation ; 

 time will show how much will be left of it and its reputation as 

 the exciting cause of putrefaction. I leave these sentences as 

 they were originally written, only adding that Hauser has since 

 shown that Cohn's Bacterium Termo is a collective species, and 

 has resolved it into three kinds ; but a closer comparison of 

 these has still to be made (51). I now conclude with it the series 

 of examples of saprophytic Bacteria. 



X. 



Parasitic Bacteria. Tlie phenomena of parasitism. 



We now pass on to the second category of Bacteria, distin- 

 guished above on page 65 by their parasitic mode of hfe. 

 The term parasite is applied in biology to the living creatures 



