FORMATION OF AMMONIA. 69 



Pigment production appears to be lessened by merely in- 

 frequent transfers of the agar culture. 



The Bact. prodigiosum at 37° forms no pigment; if 

 grown at this temperature for a long time with constant 

 transfers, the power of pigment formation is, even under 

 favorable circumstances, lost for many generations (Schot- 

 telius). 



Very interesting experiences with pigment=forming 

 cultures of varieties which usually produce colorless 

 growths are scattered through the literature; for ex- 

 ample, Fawitzky regarding yellow to rusty-red colonies of 

 Streptococcus lanceolatus; Kruse and Pasquale on colored 

 varieties of the Streptococcus pyogenes (Ziegler's Beitrage, 

 xn) ; also the experience recently published by Kutscher, 

 according to which a pseudoglanders bacillus, when ob- 

 tained from the animal, in the primary culture upon 

 serum develops a bright orange-red growth, but after a few 

 transfers the red color is completely exchanged for a white 

 one (Z. H. xxi, 156). Perhaps still more important is 

 the observation, which is easily made, that, from some in- 

 ternal condition, at times colored and colorless colonies 

 of the same variety grow side by side upon a plate; for 

 example, in Bact. kiliense. R. O. Neumann has, by selec- 

 tion, grown from the Micr. pyogenes a aureus white, yel- 

 low, and red varieties (A. H. xxx, 1). 



An analogue to this variation from internal causes is re- 

 lated by F. Hildebrand, who observed in a stock of Iris 

 florentina, which always bore pale-blue flowers each year, 

 the sudden appearance of two flowers presenting dark 

 violet portions arranged in sectors (Ber. d. deutsch. bot. 

 Gesell., 1873, 476). 



2. The Formation of Ammonia and Urea=fermentation. 



According to Sommaruga (Z. H. xn, 273), aerobic bac- 

 teria growing in non=saccharine nutrient media always 

 form an alkali from albuminous bodies. 



When sugar is present, most varieties, besides produc- 

 ing alkalis, form acids from the sugar. In this way is 

 explained the fact that many young cultures of bacteria at 

 the beginning are neutral or faintly acid in reaction because 



