300 PHENOMENA OF PUTREFACTION. 



MnUer-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 alkalis, 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 examina- 

 tion was found capable of producing an enzyme able (like pepsin) to 

 dissolve fibrin in presence of an acid. According to FERMI'S (III.) 

 results, the excretion of the proteolytic enzyme occurs, as a rule, 

 only when albumin 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 proteolytic 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 cultures, 

 an easy method proposed by FERMI (IV.) being employed. A 

 so-called Thymol-gelatin is prepared in the following manner : 

 Water saturated with thymol is qualified with 5-10 per cent, of 

 purest gelatin, and after being warmed on the water-bath is poured 

 into test-tubes (10 c.c. in each). The tubes are kept in a vertical 

 position, and are ready for immediate use as soon as the contents 

 have set. The thymol present therein will prevent any develop- 

 ment of bacteria. A large stock of these tubes can be prepared, 

 and the contents preserved from desiccation by placing the (open) 

 tubes, mouth downwards, in a covered glass vessel containing a 

 little distilled water. The liquid to be examined is filtered to re- 

 move any solid particles. A few c.c. are then placed in one of the 

 thymol-gelatin tubes, and a little thymol is added to prevent the 

 development of any bacteria already present in the sample. The 

 tube being then left to stand at room temperature, the presence of 

 any proteolytic enzyme in the sample will be revealed in a few 

 days by the liquefaction of an appreciable stratum of the gelatin. 

 To enable this change to be reliably ascertained a mark is made 

 on the tube at the time of filling, to denote the level of the gelatin. 

 The risk of the gelatin becoming dissolved by any large percentage 

 of acid or alkali present should be obviated by neutralising the 

 sample before commencing the experiment. Liquids containing 

 substances such as tannin, glycerin, &c., capable of preventing or 

 retarding the solution of the gelatin, are unsuitable for use. This 

 simple method may also be employed as an approximate quantitative 



