137 



the cn^ganism, and is insoluble in wiitor ])ecause it is dissolved in an oil 

 secreted by the cells. The small size of the rods and the minute 

 quantity of pio-ment in each one. has made it impossible to decide 

 whether the color is lodo-ed in the eell wall or in the cytoplasm itself. 

 In whichever plaee. it appears to be uniformly distributed. 



The intensity of the color depends, of course, on the density of the 

 growtli and also to some extent on its ao-e and on the nature of the 

 culture medium. It is always a distinct yellow. In the host ])lant it 

 is chrome yellow to pale cadmium. It is also })rioht yellow on many 

 culture media, especially when grown in the dark. e. g. . gamboge, 

 chrome yellow, or canary yellow. Occasionally, in cultures, it has 

 been as pale yellow as primrose or maize yellow, but this has been the 

 exception, and in some of these very pale cultures many involution 

 forms were present. On some media, V)ut not on all. old cultures be- 

 came brownish or dirty yellow. In such cultures the slime has been 

 dull yellow, dirty yellow, dark yellow, brownish yellow, ochraceous, 

 and between ocher yellow and tawny olive. In young cultures, and 

 in old cultures in which the brown stain was not detected the following 

 shades of yellow have been seen: Primrose, maize, Naples yellow, wax 

 yellow, gallstone yellow, satiron yellow, butf yellow. Indian yellow, 

 gamboge, chrome yellow, deep chrome, lemon yellow, and canary yel- 

 low. The color was very dull in potato broths, but the whitish rim 

 from such tubes made a homogeneous bright yellow growth when 

 rubbed on suitable culture media. The color was also dull yellow in 

 acid (unneutralized) beef broths, but in alkaline (soda) ones of the same 

 origin it was bright (canary) A^ellow. The color was bright yellow in 

 strongly alkaline gelatin and also in cane-sugar gelatin Avhich had been 

 aciditied with malic acid. Excess of malic acid in the gelatin appeared to 

 favor the development of the color, it being decidedly brighter in +54 

 than in +36 gelatin. The color did not appear to be any brighter when 

 the organism was grown in the ice chest at %^ to 12^ C. than when 

 grown (in an equally dark place) at room temperatures of 25^ to 30^ C. 



This color appears to be an oxidation product. It forms abundantly 

 only in organisms near the surface of solid and fluid cultures. It is 

 bleached by reducing agents, and regains its color after these have 

 been removed. It does not form so abundantly when the organism is 

 grown on suitable media in air containing a considerable reduction of 

 free oxygen, i. e., on potato or coconut in nitrogen or carbon dioxide 

 mixed with air. In these gases, when pure, there is no growth. In 

 partial vacuum growth is less abundant and the color is paler yellow 

 than in air. The same is true in nitrogen containing some oxygen, 

 i. e.. in air with the oxygen incompletely removed. (See Aerobism.) 



The following substances l)leiu-h this color: Sulphuric ether, chloro- 

 form, turpentine. bcMizinc. l)cn/()l(\ xylol, toluol. car))on bisulphide 



