566 Bulletin 167 



the only change which could be noted being- its scarcely percep- 

 tible browning or greening. Clearing without coagulation oc- 

 curred sooner or later with all strains, and was complete in from 

 1 in 5 months' time. Cultures of strain CXL, in particular could 

 not be distinguished from the control tubes until about 3 months 

 after inoculation, when clearing without coagulation began to be 

 apparent. This reaction was completed in from 4 to 5 months. 

 Repeated trials with recovery of the organism showed that this 

 clearing of the medium was not due to contamination. (Compare 

 action of this organism on milk with its action on gelatin j. The 

 only evidence of growth with strains Ps. longa, Ps. mesenterica, 

 and Ps. putrida until after a month had elapsed, was a scarcely 

 perceptible browning of the medium and a thin scum. 



8. Litmus milk. — To freshly centrifuged milk with a reac- 

 tion of -(-to to -(-12 Fuller's scale was added 2% of a saturated 

 aqueous solution of Merck's chemically pure blue litmus ; the 

 medium was then filtered, tubed and sterilized by the intermittent 

 method. When ready for use the milk had a rich lavender color. 



On this medium all strains developed an alkaline reaction. 

 which, when digestion commenced, was succeeded by one of an 

 acid character. The groups already referred to on gelatin and 

 milk were likewise differentiated here. 



The first group, rapid liquefiers and rapid digesters, showed 

 an alkaline reaction at the outset which soon gave place to an 

 acid reaction when digestion commenced. As digestion pro- 

 ceeded, a purple to a reddish coloration advanced into the sub- 

 stratum, the latter becoming first blue, then purple and red, 

 finally bleaching to a straw or amber color when digestion was 

 complete. The surface layers were more or less greenish, espe- 

 cially with Ps. fluorescens, CXII, CXLVIII. Upon agitation of 

 the tubes when digestion was completed, the medium became 

 olive green throughout. To this first group belong Ps. fluores- 

 cens, CXII, CXV, CXLVITT, and XXXVI. Ps. mesenterica on 

 this medium reacts more like the second group. 



