LABORATORY AND GREENHOUSE STUDIES. 



81 



Cultures with peptone and dextrose plus neutral red were made in 

 ordinary test tubes. The check was an orange-red color. The 

 culture tubes became in four days a magenta. In nine days they 

 were a deep magenta with the exception of tube No. 1, which had 

 paled to an orange red. 



The change to an orange-red color may be accounted for by the 

 production of ammonia, a small amount of which is found in peptone 

 cultures of this organism. (See p. 93.) 



This experiment was repeated with the same results. The color of 

 the culture solutions (except No. 1, almost bleached) in transmitted 

 light corresponds to Tyrian rose, tint No. 3, Repertoire de Couleurs, 

 Publie par la Societe Franpaise des Chrysanthemistes. 



Cultures without dextrose were made. In four days these still re- 

 mained a pink color, though a trifle paler than the check. In nine 

 days all were orange red. 



This experiment was repeated with the same result. The color of 

 the culture corresponded to reddish terra cotta, tint No. 2, Repertoire 

 de Couleurs. The check tube very closely corresponded to the red- 

 dish old rose, tint No. 4. 



In none of these cultures in peptone solutions with neutral red in 

 straight test tubes was there any of the canary-yellow color pro- 

 duced. This is undoubtedly due to the strictly aerobic condition of 

 the straight tube containing a liquid, while in the straight tube with 

 the solid agar or in the fermentation tube anaerobic conditions 

 existed which apparently are necessary for this canary-yellow re- 

 action. The change of color under aerobic conditions with and with- 

 out dextrose was caused by the acid production. In the presence of 

 sugar acids are produced which change neutral red to a magenta 

 color. The production of acid was not tested except in the presence 

 of dextrose, saccharose, lactose, and glycerin; but gas, which is an 

 indication of acid production, was observed to form in the presence 

 of levulose, galactose, and mannit. 



Table XIII. — Growth of various cultures of March 18, 1910, on agar, containing neutral 



red and dextrose, at 37° C. 



6389°— Bul. 228—12 6 



