TEXT-BOOK OF BACTERIOLOGY. 163 



itself within very narrow limits, but a return to the normal condi- 

 tions of growth soon fully restores the interrupted power. 



The formation of coloring matter is also capable of artificial 

 attenuation. The M. prodigiosus, as we have said, can only thrive 

 with difficulty at high temperatures, chiefly on account of its sapro- 

 phytic nature. If it is compelled to grow for many generations at 

 the temperature of the incubator, the red pigment disappears more 

 and more, and it is even possible, as Schottelius has shown, to get 

 perfectly colorless white cultures. Sour bouillon produces similar 

 effects, but the loss of developing power is in both cases only 

 temporary. Two or three transplantations to potato or agar-agar 

 at ordinary temperature suffice to restore strength and beauty to 

 the pigment and counteract the previous attenuation. The pig- 

 ment is formed in the cells as a chromogenic substance, a white 

 body, so that it cannot be seen in them. It is only outside the bac- 

 terium and in contact with the oxygen of the air that the color 

 develops, appearing in clearly -visible granules and extending to its 

 immediate neighborhood. Its formation, therefore, ceases as soon 

 as the access of oxygen is diminished or made impossible, and in 

 our colonies it is only developed at the surface. 



The absence of light is without influence on the production of 

 the pigment. 



Nothing is known as to the precise chemical nature of the pig- 

 ment. The fuchsin film already mentioned reminds one of the be- 

 havior of the anilin colors. 



The coloring matter is insoluble in water, soluble in alcohol 

 and ether; when treated with acids it becomes paler and light red; 

 if it is then mixed with strong alkalies, such as ammonia, for in- 

 stance, it regains its former appearance. 



It is further to be noted that both in its growth on gelatin 

 and on the potato the prodigiosus emits that penetrating and un- 

 mistakable odor of trimethylamin which is so characteristic of 

 herring-brine. In milk the prodigiosus gradually causes the sepa- 

 ration of casein, and gives to this food medium a deep red color, 

 without causing further decomposition. It causes a solution of 

 sugar to ferment, forming alcohol and carbonic acid. 



The soluble products of the prodigiosus produce some effect on 

 the bodies of animals. Grawitz and DeBary have shown that large 

 quantities of prodigiosus culture are able to produce inflammatory 

 symptoms; Eoger discovered the interesting fact that animals 

 which are otherwise not susceptible to malignant oedema may be 

 infected by the bacteria of this disease if, at the same time, 1 or 2 

 c.cm. of a prodigiosus culture be injected; Pawlowsky, lastly, showed 



