192 AIDS TO BACTERIOLOGY 



5. Steatctyiic, splitting fats into fatty acids and glycerin. 

 Lipase (steapsin), which occurs in the pancreatic juice 

 and in many plants, is an example of this class. 



6. Peptolytic, splitting proteoses and peptones into 

 polypeptides and amino-acids. 



Other groups bear oxygen and produce oxidation 

 (Oxydases), produce reduction (Reductases), or break off 

 amino-groups from amino-compounds (Deamidases). 



While some enzymes can act alone, others require the 

 stimulus of an activating agent or co-enzyme (p. 163). 

 Antecedent substances (zymogens) which produce the 

 enzyme exist in the cells. While an enzyme will only act 

 under specific conditions on a specific substance, its 

 power in this limited sphere is inexhaustible, as is that 

 of an inorganic catalyst. Enzyme action is generally 

 reversible, and during an analytic or splitting reaction 

 there goes on at the same time a synthesis reproducing 

 the original substrate. 



Tissue enzymes may be defensive; the blood of a 

 pregnant woman elaborates a specific defensive enzyme 

 in response to the entry of placental proteins into her own 

 blood-stream. 



The Sulphur Bacteria. 



David Ellis classes under this heading those organisms 

 which have the power of assimilating sulphuretted 

 hydrogen and effecting its oxidation: the Beggiatoa (see 

 p. 160); the Thiothrix, which differ from the Beggiatoa 

 in being non-motile, and having a common thread mem- 

 brane; the Thiophysa, which form no threads; and the 

 Purpur bacteria, which contain a colouring matter in the 

 cells, bacterio-purpurin, which seems to have a function 

 in abstracting oxygen from the medium. 



The Iron Bacteria. 



These organisms occur in ferruginous waters, and 

 convert the soluble bicarbonate, FeH 2 (CO 3 ) 2 , into ferric 

 hydroxide, Fe 2 (OH) 6 , the organisms becoming coated 

 with the latter. In addition to Crenothrix polyspora 

 and Cladothrix dichotoma (p. 160), the following organisms 

 act in the manner indicated: 



Leptothrix ochracea (Chlamydothrix ochracea) averages 

 in length from 100^ to 120 /t. Reproduction takes place 



