230 THE PHENOMENA OF PUTREFACTION 



to be erroneous. A few observations on this point were also made by E. 

 DUCLAUX (XI.). 



170. Proteolytic Enzymes. 



All the fission fungi (with the few exceptions given in chapter xxxiii.) 

 require nitrogenous nutriment for the construction of their cells. Such of 

 these nitrogenous materials as are soluble in water, and therefore diffusible 

 through the cell-wall by osmosis, need not be referred to here. Mostly, how- 

 ever, the nutriment presented to the bacteria is insoluble in water, and this is 

 particularly the case with the protein albuminoids. To enable these latter to 

 supply the nitrogen required for the elaboration of the bacterial plasma they 

 must first be converted into soluble compounds, a task which is effected by the 

 proteolytic enzymes. So far no comprehensive study of these active bacterial 

 secretions has been made, and at present our knowledge is chiefly confined to 

 the enzymes dissolving gelatin and fibrin. A new classification of the bacteria 

 into two groups, the liquefactive and non-1 iquef active towards gelatin, according 

 to the presence or absence of a proteolytic enzyme, has obtained currency in 

 practical bacteriology since the introduction of the Koch system of plate- 

 cultures. 



We are indebted to CL. FERMI (IT.) for the first extensive series of pure 

 culture investigations on this point. He proved that a gelatin-dissolving 

 enzyme is formed in cultures of the following species of Schizomyceles : 

 Bacillus sublilis, B. anlhracis, B. megatherium, B. pyocyaneus, Vibrio choleras 

 asiaticce, Vibrio Finkler~ Prior, Micrococcus prodigiosus, M. ascoformis, M. 

 ramosus, spirilla from cheese, &c. Fibrin is dissolved as well as gelatin, but less 

 readily than the latter. Egg-albumen and coagulated blood-serum offer greater 

 resistance to these bacteria, thus indicating that pepsin is not present. Keasons 

 exist for assuming that the enzymes produced by the said microbes are not all of 

 the same kind, one conclusive indication being afforded by their behaviour under 

 different temperatures. Thus, for example, the proteolytic enzyme produced by 

 Micrococcus prodigiosus is rendered inactive (in solution) by a temperature of 

 55 C., that from B. pyocyaneut by 60 0., that from B. anthracis by 65 C., 

 and that from Vibrio F 'inkier-Prior not below 70 C. Similar differences of 

 behaviour are observed towards acids, bases, and poisons. A fundamental 

 difference exists between these enzymes and pepsin, since whereas the latter is 

 extremely sensitive towards alkalies, and is absolutely incapable of dissolving 

 albumin except in presence of free hydrochloric acid ; the bacterial enzymes in 

 question act on fibrin in neutral or faintly alkaline solutions only, though they 

 will attack gelatin even when the liquid is slightly acid (0.5 per cent. HC1). On 

 this latter account they more nearly resemble trypsin, i.e. the enzyme secreted 

 by the gastric glands. None of the Schizomycetes under examination was found 

 eapable of producing an enzyme able (like pepsin) to dissolve fibrin in presence 

 of an acid. According to FERMI'S (HI.) results, the excretion of the proteolytic 

 enzyme occurs, as a rule, only when albumen is present in the nutrient medium. 

 Two only, of all the species examined by him, exhibited any variation in this 

 respect, viz., Micrococcus prodigiosus and B. pyocyaneus, which yielded a proteo- 

 lytic enzyme when cultivated in a mineral nutrient solution qualified with 

 glycerin or mannite. 



It has long been known that antiseptics in small doses exert no injurious 

 influence on the action of enzymes. On this point some conclusive investigations 

 were published by FERMI and PERNOSSI (I.), and use is made of this property in 

 testing for the presence of a proteolytic enzyme in samples of liquids or bacterium 

 pultures, an easy metho4 proposed by FERMI (IV.) being employed, A so- 



