28 



naked eye, but there was no liquefaction. Ten da3^s later the colonies 

 were decidedl}^ larger, l)ut otherwise much the same. The margins 

 were still well defined and regular and there was no liquefaction. In 

 less crowded plates of the same gelatin (ii(»0 to 600 colonies per field) 

 at the end of 5 daj^s (13° to 16° C.) the buried colonies were like those 

 just described, only larger — 28 by 28yM to 56 by 61yU, the greater num- 

 ber being 32 by 32/^ to 36 by 36yM. Ten days later, at 12° to 16° C, 

 the colonies had doubled in size, were round, roundish, or broadly 

 elliptical, pale and fineh^ granular (16 mm., 12 oc), with clear, well- 

 defined margins. The colonies in the deeper layers of the gelatin were 

 decidedl}^ smaller than those near the surface. The largest of the 

 buried colonies, including some of the clumpy compoimd ones, were 

 then a feeble tint of yellow. This color was onl}' visible in the upper 

 colonies. No spindle-shaped colonies were visible. Only two small 

 pits of liquefaction were observed. These arose from surface colonies, 

 of which very few were visible; i. e., the buried colonies did not easily 

 break through and come to the surface, and free access of air appeared 

 to be necessar}^ for liquefaction. 



None of the man}- pure cultures of Ps. Jiyacinthi in gelatin developed 

 any gas bubbles (see Fermentation tubes), and the gas bubbles observed 

 b}^ Dr. Wakker in his gelatin cultures must be attributed to some 

 contaminating organism.^ Contrary, also, to Dr. Wakker's statements 

 the gelatin did not become brown. In all of the gelatin cultures 

 (tubes under observation from 3 to 6 weeks or more) it remained free 

 from browning; i. e., was of the same color as when inoculated. 



Ps. co/mpestris and Ps. phaseoli both liquefy gelatin, and more readily 

 than Ps. hyacinthi., but none of them are rapid liquefiers. 



In nutrient gelatin stock 178, consisting of 1,000 c. c. stock 473b 

 (beef broth acidity +17) and 100 grams of gelatin with 17 c. c. of 



^ NaOH, Ps. stewartt, made a good growth. At the end of the fort}"- 



first day (temperature 17° to 22° C.) there was along the track of the 

 needle puncture a thin line of growth, increasing towai'd the surface, 

 and a dense, rather dry, and slightly roughened bright buff-yellow 

 surface growth 7 mm. in diameter, but no liquefaction. 



^ The only gas that ever appeared in any of my cultures was in one of four gelatin 

 tubes made June 23, 1897, in Dr. Wakker's manner, i. e., directly from the yellow 

 interior of a disorganized bundle in an otherwise sound bulb scale. This tube was 

 inoculated with great care to avoid external contaminations, and it appeared to be 

 all right for some time, but after 22 days a gas bubble appeared in the gelatin near 

 the bottom of the stab (temperature 12° to 18° C. ). This was then the only evidence 

 of anything wrong, but two weeks later the nature of the contamination became 

 perfectly plain, the gelatin becoming fluid to the walls of the tube in the upper 

 two-thirds, the upper part of the liquefied i^ortion Ijeing greenish fluorescent and 

 the bottom covered with a copious whitish precipitate with a little of the yellow 

 Ps. kyacinthi mixed in. Undoubtedly this was an aerial contamination, as Ps. hyacinthi 

 is never greenish fluorescent. 



