CHEMICAL CHANGES 103 



Salkowski ^ inoculated fibrin with putrefactive bacteria and 

 kept it in chloroform water. It remained sterile for an un- 

 imited time, but nevertheless underwent solution with the 

 sual products, due to an enzyme secreted by the bacteria at 

 rst. Hoppe-Seyler describes several fermentations which are 

 nitiated by bacteria, but continue after the destruction of the 

 rganisms by ether.^ 



Dr. Armstrong^ proposes the terms zymosis for fermenta- 

 ion by living organisms, and enzymosis for change by enzymes 

 r unorganized ferments. The former class of changes would 

 e intracellular y or within the cell, under the immediate action 

 f the protoplasm ;* the latter class would be external or extra- 

 ellular. By such means bacteria are able to produce effects 

 hich are quite out of proportion to their size or numbers. As 

 n example of intracellular action, Wroblewski^ states that 

 with Buchner's yeast-extract filtration through a Berkefeld or 

 sandstone filter diminishes, and through a Chamberland filter 

 entirely removes, the fermenting power ; this shows that in 

 fermentation by yeast cells the zymase remains in the cells and 

 does not diffuse into the sugar solution. If the cells are 

 collected on a sandstone filter, fermentation in the sugar 

 solution ceases; Wroblewski is therefore of the opinion that 

 the sugar solution passes into the cells and is there fermented. 

 Alcohol and carbonic acid, accordingly, are true excreta of the 

 yeast cells. 



Enzymes are formed not only by bacteria, but by moulds,, 

 larger fungi, and also by plants and animals, but have not as 

 yet been prepared artificially. Free oxygen is not necessary 

 for their production.^ The mode of action is still imperfectly 

 understood; probably they act like some inorganic bodies by 

 forming unstable compounds with portions of the organic 

 molecule, which then break up, leaving the substance 

 hydrolysed, and freeing the enzyme to act again. As they 

 are of such value, it will be useful to give a list of the more 

 important ; many of them, or their analogues, must occur in 

 sewage, since the changes they produce are present. We may 

 divide them into groups. 



^ Zeit. Phys. Chem., 1899, xxvii. , 305. ^ PJluger's Archiv, xii., i. 



^ Transactions of the Chemical Society, June, i8go, p. 528. 



^ Martinus Beyerinck uses the term " katabolic " for changes brought about by 

 the direct action of living protoplasm, having proved that dead bacteria have no 

 effect on certain compounds which are decomposable by enzymes {Proc. K. Akad, 

 Wetensch., Amsterdam, 1900, ii., 495). 



^ Journ. Prakt. Chemie., 1901, ii., 64, p. i. 



^ Godlevvski, Bull. Acad. Sci. Cracow, 1901, 227. 



