28 



lowing Mr. Fuller's scale ^ as +40 gelatin, +20 gelatin, o gelatin (neu- 

 tral to phenolphthalein), and —'25 gelatin. The lituuis reaction of 

 these gelatins was as follows: +40, feebly acid; +20, very feebly 

 alkaline; 0, strongly alkaline; —25, ver}' strongly alkaline. 



As already stated, the best growth of Ps. ht/acl/tt/a, when pep- 

 tonized beef broth was used, was in the gelatin (stocks 205 and 244c). 

 the next best was in the +20 gelatin. The difference in growth on 

 these two gelatins was more striking at lirst than later on, the organ- 

 ism being al)le to partially overcome the inhibiting substances in the 

 +20 gelatin. The growth in +40 and — 25 gelatin fell far behind 

 that in the other two. One was too acid and the other too alkaline.'^ 

 These tubes were kept in a cool box at temperatures varying from 10^ 

 to 22- C. (most of the time 13- to 18- C). In all the stab cultures the 

 growth was best in the upper part, gradually fading out in the depths. 

 The yellow color was also best developed near the surface, Avhere there 

 was freest contact with the air. There was no indication of yellow in 

 the growth in the depths of the stabs. 



The following notes represent the usual liehavior of stab cultures in 

 15 per cent nutrient gelatin made neutral to phenolphthalein : 



Stock 244c (10 c. c. of very clear gelatin in tubes 16 mm. in diameter) : Stab made 

 June 2, from a fluid culture 11 days old (cauliflower broth); one needle-thrust the 

 whole length of the gelatin (5 or 6 cm.); tube kept in the cool box at temperatures 

 varying from 10° to 22° C. (most of the time 13° to 18° C). June 4 (range of tem- 

 perature, 17° to 22° C. ): A whitish thread distinctly visible one-half way down; it 

 fades out gradually. June 5 (temperature, 13° to 15° C. ) : Stab whitish, feeble, visible 

 three-fourths of the way down. June 8 (temperature, 13° to 16° C.) : Stab begins to 

 fade out two-thirds down; growth decidedly better than in the -^20 gelatin — at least 

 twice as much growth; slight liquefaction — i. e., a pit at the mouth of the stab, 3 mm. 

 wide and 2 mm. deep. June 10 (temperature, 10° to 13° C. ) : Rather better growth 

 than in the -f 20 gelatin, but fading out in the depths; no marked increase of lique- 

 faction; surface growth pale yellow, rather dry looking, about 3 mm. in diameter; 

 surface irregular. June 13 (temperature, 12° to 16° C): A better growth than in the 

 -f20 gelatin, but fading out in the depths; surface growth about 4 mm. in diameter, 

 pale yellow; pit of liquefaction 4 mm. wide and 2 mm. deep. June 18 (temperature, 

 14° to 18° C.) : Growth a little better than in the -^20 gelatin, but not now strikingly 

 so; the stab fades out in the depths; surface growth pale yellow; pit of liquefaction 

 only 5 or 6 mm. wide and 3 mm. deep; growth in the +40 gelatin is so slight as to 

 be easily overlooked; growth in the — 25 gelatin is confined to the surface and there 

 is no liquefaction. June 28 (temperature, 13° to 19° C. ): The pit of liquefaction is 

 now 1 cm. deep and 1 cm. wide; it is a larger pit than in the -f 20 gelatin, and there 

 is more growth in it, and also more in the depths of the stab, but the latter fades out 

 at the bottom; the surface growth is distinctly yellow; in the +40 gelatin there is 

 a barely visible growth in the upper part of the stab, a pit of Hquefaction 3 to 4 mm. 

 wide and 4 to 5 mm. deep, with a little whitish sediment at the bottom; in the — 25 

 gelatin there is no visible stab, but a distinctly yellow surface growth 5 mm. in 

 diameter, and a feeble liquefaction under it. 



'Fuller: On the i)roper reaction of nutrient media for ])acterial cultivation. Jour. 

 Am. Public HeaUh A.-^sociation, Oct., 1895, p. 381. 



^For the varying behavior of Pn. nnnpcfitris in tlieso four gelatins, see plate in 

 The American Naturalist, March, 1SV»9. 



