40 CULTURE MEDIA. 



made for me by Dr. L. L. Van Slyke in the chemical laboratory of 

 Johns Hopkins University : The weight of the fluid obtained from 

 six nuts averaged 339.1 grammes. The specific gravity averaged 

 1.02285. The amount of water averaged 95 percent; the amount 

 of inorganic ash, 0.618 per cent; the amount of glucose, 3.97 per 

 cent ; the amount of fat, 0.119 per cent ; the amount of albuminoids, 

 0.133 percent. 



As this fluid is contained in a germ-proof receptacle, no steriliza- 

 tion is required when it is drawn off with proper precautions in the 

 little flasks heretofore described. 



Hydrocele fluid has been used as a culture medium, and many 

 bacteria multiply in it abundantly. 



Other natural culture media are found in animal and vegetable 

 substances, which are used, either cooked or raw, as solid sub- 

 strata upon which bacteria may be cultivated. One of the most use- 

 ful of these is the potato, which is a favorable medium for the de- 

 velopment of numerous species, and upon which (cooked) many of 

 them present characters of growth which are so distinctive as to aid 

 greatly in the differentiation of species. 



Other tubers, roots, or fruits may also be used as solid media, or 

 their juices extracted and employed as liquid media. Cooked fish 

 and meats of various kinds are also suitable media for certain spe- 

 cies e.g., the phosphorescent bacteria grow very well upon the sur- 

 face of boiled fish, and in a dark room give off a bright, phosphores- 

 cent light. 



Eggs, sterilized "by boiling, have been used by some bacteriolo- 

 gists, especially for the cultivation of anaerobic species. 



ARTIFICIAL CULTURE MEDIA. A great variety of liquid media 

 have been employed by bacteriologists, the most useful of which are 

 infusions of beef or mutton, with the addition of a little peptone. 

 But Pasteur has shown that some species of bacteria will grow in a 

 medium which does not contain any albuminous material, nitrogen 

 being obtained from salts containing ammonia. 



Pasteur's solution, which is rarely used at present, contains : 

 Distilled water, one hundred parts ; cane sugar, ten parts ; tartrate 

 of ammonia, one part, with the addition of the ashes from one 

 gramme of yeast. 



Cohn modified this by leaving out the cane sugar, which favors 

 the development of moulds. These fluids are not, however, in- 

 tended for general use in the cultivation of bacteria, but to demon- 

 strate certain facts relating to their physiology. 



Infusions of meat, or " flesh water," are made by chopping fine 

 lean beef or mutton (one pound) and covering it with water (one 

 litre). This is placed in an ice chest for twenty-four hours, and the 



