PRODUCTS OF VITAL ACTIVITY. 129 



"cause liquefaction of gelatin " tryptic enzymes " made by Fermi r 

 in the laboratory of the Hygienic Institute of Munich (1891), the fol- 

 lowing results were obtained : 



The enzymes were not obtained pure, and their isolation from 

 other proteids present in the cultures was found to be attended with 

 great difficulties, but their ferment action was studied and was found 

 to be influenced by various conditions. 



All were destroyed by a temperature of 70 C., but the enzymes 

 produced by various liquefying bacteria differed considerably as to 

 the temperature which they were able to withstand. Some were de- 

 stroyed by a temperature of 50 to 55 C. Bacillus megatherium, 

 Bacillus ramosus, Staphylococcus pyogenes aureus ; some by a tem- 

 perature of 55 to 00 C. Bacillus subtilis, Bacillus pyocyanus, Bacil- 

 lus fluorescens liquefaciens, Sarcina aurantiaca ; some by 65 to 70 

 C. Bacillus anthracis, Spirillum cholerae Asiaticse, Spirillum of 

 Finkler and Prior, Spirillum tyrogenum. 



These enzymes, like the previously known pepsin, trypsin, and 

 invertin, do not dialyze. 



Only a few of these bacteria enzymes acted upon fibrin, and no 

 action was observed upon casein or upon egg albumen. 



Their liquefying action upon gelatin was prevented by the action 

 of sulphuric acid, and to a less degree by nitric acid, but was not in- 

 terfered with by acetic acid. 



The liquefying bacteria, as a rule, only produce enzymes when 

 cultivated in a medium containing albumen. 



These enzymes are not produced by a solution of the protoplasm 

 of dead bacterial cells, but are a product of the vital activity of liv- 

 ing cells. 



Among the numerous liquefying bacteria known to bacteriolo- 

 gists we may mention the following species as deserving the student's 

 special attention : Staphylococcus pyogenes aureus (No. 1), Staphylo- 

 coccus pyogenes albus (No. 2), Sarcina lutea (No. 227), Sarcina au- 

 rantiaca (No. 226), Bacillus anthracis (No. 45), Bacillus pyocyanus 

 (No. 95), Bacillus subtilis (No. 379), Bacillus indicus (No. 283), Ba- 

 cillus prodigiosus (No. 284), Spirillum cholerse Asiaticae (No. 155), 

 Spirillum of Finkler and Prior (No. 156), Proteus vulgaris (No. 97). 



Production of Acids. Numerous bacteria give an acid reaction 

 to the media in which they are cultivated, and the acids produced 

 are various lactic, acetic, butyric, propionic, succinic, etc. 



The power to produce an acid is well shown by adding to neu- 

 tral or alkaline culture media a solution of litmus. The change in 

 color due to the formation of an acid may be followed by the eye, 

 and comparative tests may be made to aid in the differentiation of 

 similar bacteria. 

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