141 



tins employed. On the other hand, it is pro])able that the browning 

 he observed arose from the presence of some intruding- organism — 

 e. g., the one which produced gas bubbles in his gelatin. 



The following shades of brown were observed: (1) A slight browning 

 (yellow banana pulp, 55 days; water around potato cylinders, 31 days); 



(2) feeble brown (white turnip, 22 days; water around potato cylin- 

 ders, 24, 37, 67 days; washed potato starch cooked in distilled water 

 with 1 per cent Witte's peptone, 73 days; hyacinth broth, 59 days); 



(3) pale brown (yellow turnips, 23 days; one-half strength potato 

 broth with 1 per cent Witte's peptone, 41, 59, 73 days; the same with 

 malic acid, ^1, 73 days); (4) brownish (a potato cylinder with 500 mgs. 

 Merck's diastase of malt absolute, 41 da3^s); (5) feeble reddish brown 

 and later brownish white with the slightest trace of pink (washed 

 potato starch with 4 per cent peptone water and Taka diastase, 44, 73 

 days; also the same stain without the diastase ])ut feebler); (6) tawny 

 olive (white turnips, 40 days); (7) paler than tawny olive (yellow tur- 

 nips, 22 days); (8) ochraceous (white radish, 50 days); (9) russet (white 

 turnips, 40 days); (10) between russet and burnt umber (yellow turnips, 

 40 days); (11) light burnt umber (white turnips, 49 days); (12) midway 

 between burnt umber and mummy brown (yellow globe turnip, 50 days); 

 (13) burnt umber (yellow globe turnip, 64 days); (14) sienna with a very 

 slight admixture of brown (radish, 49 days); (15) dark brown (skin of 

 yellow banana, 56 days). 



The formation of this pigment appears to depend on the presence of 

 certain highly organized nitrogenous bodies — e. g,, albuminoids or pep- 

 tones. Whether it is produced inside of the bacterial cell and dissolved 

 out, or is formed in the substratum by the chemical action of colorless 

 substances excreted from the cells, as seems more likely, could not be 

 determined. Its formation also appears to depend on the presence of 

 free oxygen, as in one instance, in an old culture on rutabaga (50 days) 

 it was observed that the upper part of the substratum was distinctly 

 browned, but in that part protected from the air (the lower one-half 

 of the cylinder, in water grown full of the yellow slime and solidified) 

 it was not browned. 



1\. steioarti grayed potato cylinders, but in two months it formed 

 no brown pigment in tubes of radish, ruta})aga, or yellow globe turnip. 

 In from 6 weeks to 2 months P.^. cnmpestris stained these same crucif- 

 erous substrata various shades of l)rown — e. g., (1) raw sienna, (2) a 

 color })etween russet and cinnamon rufous, (3) a color between vussct 

 and tawny olive, (4) raw umber, (5) burnt umber, (6) dark burnt 

 uml)er, (7) nuunmy brown. 



These brown pigments are also believed to be in some way connected 

 with the presence of sulphur compounds and of taiuiins or related 

 bodies in the plant or substratum, and with the formation of hydrogen 

 sulphide and annuonia })y the bacterial organism. 



