542 



Drs. T. L. Brunton and A. Maefadyen. 



" The Ferment-action of Bacteria." By T. Lauder Brunton, 

 M.D., F.R.S., and A. Macfadyen, M.D., B.Sc. Received 

 March 23— Read April 4, 1889. 



In the course of the research the following micro-organisms were 

 used : — 



1. Koch's comma spirillum (Fliigge, 'Die Mikro-organismen,' 



Leipzig, 1886, p. 334). 



2. Finkler's comma spirillum (Fliigge, ' Die Mikro-organismen,' 



Leipzig, 1886, p. 382). 



3. A putrefactive micrococcus. 



4. Scurf bacillus (Klein). 



5. A bacillus isolated from milk by Dr. Klein, which for con- 



venience we may call the "Welford Bacillus." 



All of these liquefy gelatine, the two last most energetically. 

 Anthrax was not used, on account of the resistance of its spores and 

 the consequent difficulty of completely sterilising the culture media. 

 The experiments were made in each case with pure cultures. 



The first question which we tried to solve was, What is the nature 

 of the substance by which bacteria liquefy gelatine ? Is it an enzyme ? 

 There are two ways in which they might do this. They might 

 secrete some fluid which would dissolve the gelatine mechanically, 

 without altering it chemically, as saliva dissolves sugar in the mouth ; or 

 they might do it by secreting a specific enzyme, which would dissolve 

 the gelatine by altering it chemically, as the ptyalin of the saliva 

 effects the solution of starch. If the solution were effected in the 

 first way by the secretion of a mere solvent, we should expect that 

 when the microbes were removed or destroyed, either by heat or 

 chemical means, the portion of the medium already dissolved would 

 not have any extensive action on fresh media. But if it had any 

 such solvent action, it would probably continue after the solution had 

 been heated to a temperature sufficient to destroy the action of an 

 enzyme. If, on the other hand, the microbes liquefied the media by 

 secreting an enzyme, we should expect that the liquefied portion 

 would probably dissolve a considerable amount of new medium when 

 added to it, but that its solvent action would be arrested by exposure 

 to a temperature sufficient to inhibit enzyme action. 



The culture medium was made by adding to meat broth: gelatine, 

 10 per cent. ; peptone, 1 per cent. ; and sodic chloride, 0"5 per cent. 

 The reaction was rendered faintly alkaline with carbonate of soda. 

 In all the experiments Koch's methods to ensure sterile media and 

 pure cultures were followed out. 



