228 LABORATORY EXERCISES IN BACTERIOLOGY. 



is of a pale, phosphorescent type. Like pigment production, it is interrupted or modified 

 in intensity by conditions altering the vital activities of the bacteria, as temperature, 

 atmospheric relations, and various chemical agencies, and the like. Photogenic 

 bacteria are apt to be encountered in cultures obtained from salt water or salt fish ; 

 and photogenesis is most apparent and best preserved when such bacteria are grown 

 in media rich in saline elements (as nutrient gelatine made from an infusion of salt 

 fish in natural or artificial sea-water, with addition of one per cent, of peptone, one 

 per cent, of glycerine, and 0.5 per cent, of asparagin Neumann and Lehmann). 



Exercise 58. Let the instructor here demonstrate in the dark-room the 

 light production of one of the phosphorescent bacteria grown on above 

 medium. 



3. Ferments. By fermentation is meant the splitting up of complex organic 

 molecules into simpler ones through the agency of a so-called enzyme, or non-living 

 ferment, which is itself not destroyed in the process it excites. Such enzymes may 

 operate in the presence of various substances which are harmful to the bacteria them- 

 selves, and are found active in the germ-free filtrate from cultures; and are therefore 

 to be regarded as not residing in the bacterial cells, but rather as a product of elimina- 

 tion from the cells. 



(a) Proteolytic (Albumin-dissolving) Ferments. These are present in the cultures 

 of a large number of bacteria, and give rise to the common phenomenon of liquefaction 

 of gelatine media (the glue in gelatine) and blood-serum. The production of peptones 

 or propeptones is a result of such liquefaction. It may be demonstrated by a thorough 

 filtration of a liquefied gelatine culture through a porcelain filter, adding to ten cubic 

 centimeters of the filtrate 5 grams of ammonium sulphate and keeping it warm for 

 half an hour (thus precipitating all albumins but the peptones and propeptones), then 

 refiltering and testing the latter filtrate with an alkaline solution of cupric sulphate, 

 when the peptones strike with the reagent a violet color. 



Exercise 59. Plant in a flask, or a number of tubes, of gelatine medium 

 Bacillus prodigiosus, and allow the material to become completely lique- 

 fied. Then through a porcelain filter sterilized in the autoclave separate 

 the bacteria from the liquid holding soluble albumins in solution. Divide 

 the latter into two parts. To one part (10 cubic centimeters, at least) add 

 an excess of ammonium sulphate, which will precipitate all of the albumins 

 but the peptones and propeptones. Refilter and test the filtrate with 

 Fehling's solution of copper sulphate for the violet reaction of peptones. 



Add the second part of the original filtrate (free from bacteria) to a 

 fresh tube of gelatine; observe that in the course of twenty-four to forty - 

 eight hours liquefaction of the gelatine takes place from the action of the 

 bacteria-free enzyme. 



Plant a tube of gelatine each from known cultures of Micrococcus py- 

 ogenes, Bacillus coli, Bacillus typhosus, Mycobacterium diphtheria, and 

 Microspira comma. Note the results as to liquefaction in each case. 



