86 BACTERIOLOGY. 



on blood-serum they cannot utilize this material as food 

 unless some of it is first dissolved, and in this condition only 

 can it be absorbed through the cell-wall. Bacteria must 

 therefore produce proteolytic ferments analogous to those 

 made by the stomach and by the pancreatic gland. 



Many bacteria are characterized by the rapidity with 

 which they digest or dissolve albuminous matter. The liq- 

 uefaction of gelatin by certain bacteria is due to the forma- 

 tion of peptonizing ferments. Many bacteria do not liquefy 

 gelatin and this would seem to indicate the absence of this 

 class of enzymes. There is reason to believe that even 

 these organisms produce such ferments which, however, do 

 not readily diffuse into the surrounding medium. The 

 tubercle and typhoid bacilli do not peptonize coagulated 

 blood-serum and yet the cell contents in each case will show 

 a distinct, though slow proteolytic action. It has been shown 

 above (p. 84) that certain bacteria elaborate toxins, which 

 in some species, may readily pass out of the cell, whereas 

 in others they are apparently retained within the cell. The 

 same is apparently true of the bacterial ferments, which in 

 some cases easily diffuse outward (liquefying bacteria), 

 whereas in others they tend to remain within the cell. 



Bacteria, clearly, cannot absorb the insoluble starch. 

 Like the animal cell they can make use of starch as food 

 only after it has been dissolved and converted into sugar. 

 They, therefore, secrete starch-splitting or amylolytic fer- 

 ments. In some bacteria this action on starch is quite 

 marked, whereas in others it is apparently absent. The 

 action of bacteria on fats, likewise, is largely due to the 

 presence of a soluble ferment. 



It has been customary to divide the so-called ferments 

 into two groups: 



1.) Organized, formed, living, or insoluble ferments; 

 2.) Unorganized, formless, non-living, or soluble fer- 

 ments. 



