140 OUTLINES OF BACTERIOLOGY 



species may be effected by making use of a mixture prepared in the 

 following way : To a litre of water 125 grams of minced beef are 

 added. After being shaken, the mixture is allowed to stand at about 

 10 C. for a day or so, when the sap is pressed out and about 3 per 

 cent, of common salt added. The mixture is next boiled and filtered, 

 and to the filtrate 10 grams of peptone and 100 grams of gelatine are 

 added. Then caustic soda is added, drop by drop, until a very faint 

 alkaline reaction is obtained. The mixture is completed by the 

 addition of 0-5 per cent, of glycerine. By inoculating this mixture 

 with a little of the phosphorescent flesh, and then making gelatine- 

 plate cultures from the resulting growth, pure cultures may be 

 obtained. 



Physiological Considerations. It will be noticed that common salt 

 is an important ingredient of any mixture for the cultivation of phos- 

 phorescent bacteria. They will not grow in the ordinary nutrient 

 media, but the addition of even 0'5 per cent, of common salt imme- 

 diately changes the aspect of affairs, and growth and multiplication 

 actively set in. This partly explains why the sea is such a favourable 

 habitat for their multiplication. Experiments have shown that about 

 3 per cent, of common salt produces the optimum effect. If more 

 than 3 per cent, be used the resulting growth is smaller, whilst if 

 10 per cent, or more be employed no growth at all takes place. It has 

 been recently found that the salt can be replaced by a number of other 

 substances. Common salt is the chloride of sodium, and it has been 

 shown that any chloride, e.g. of potassium or of magnesium or of 

 calcium, can be substituted for it. Further, even a chloride is not 

 necessary, for instead, potassium nitrate or potassium iodide will 

 serve the purpose. 



There is no necessary connection between phosphorescence and 

 either growth or respiration. Thus, in the case of Bacterium phos- 

 phoreum, the addition of small quantities of magnesium sulphate 

 greatly increases the growth, but the phosphorescence remains very 

 weak. On the other hand, a minute addition of laevulose or glucose 

 causes an increase in the phosphorescent glow after a few seconds, and 

 in this short time there could be no perceptible change either in the 

 growth or in the respiration. Many substances, however, e.g. common 

 salt, favourably influence together the growth, the respiration and the 

 phosphorescence. 



Beijerinck has proposed to utilise these bacteria as aids in the 

 identification of certain carbohydrates and of certain enzymes. His 

 proposition was to make use of the different behaviour of Photo- 



