216 HAROLD C. ROBINSON AND LEO F. RETTGER 



grew better on the control. On the other hand, the Hofmann 

 bacillus showed a much better growth on opsine. Cultures of 

 B. prodigiosus on opsine were of a good red tinge, but in the con- 

 trol tubes were colorless. 



As smears from the opsine and the control cultures were made 

 and stained side by side on the same slide, a careful comparison 

 between the two series as to morphology and staining reaction 

 was possible. With many organisms, the stained preparations 

 from the two media were practically identical as to the morphol- 

 ogy and uniformity of the bacteria, and the nature and depth of 

 the stain. In others, however, distinct differences could be 

 detected, which were sometimes in favor of the opsine, and again 

 to the advantage of the control medium. Several Gram-positive 

 organisms showed a tendency to be Gram-negative on the opsine. 



In order to see if long continued residence in opsine would 

 induce any changes, these cultures were kept at 16° for twenty- 

 four days, then a fifth series of transplants was made to the opsine 

 and control media respectively, and the organisms stained as 

 before. The results on the opsine were somewhat more favorable 

 than before, although there was no very striking or general change. 

 Without going into much detail, it can be stated in a general way 

 that on opsine B. coli, B. pneumoniae, M. cholerae, B. avisepticus, 

 B. glycohacter (peptolyticus), Streptococcus viridans, Proteus vul- 

 garis and the diphtheria group were more typical and uniform, 

 while the control medium was the more favorable for Bad. 

 pullorum, Staph, aureus, B. prodigiosus, B. fluorescens (lique- 

 faciens) and Proteus zenkeri. On the whole, the pathogens, 

 especially those that are more difficult to cultivate on ordinary 

 media, as the diphtheria group and Streptococcus viridans, were 

 more uniform and typical in morphology, and stained better, 

 when grown on opsine than on the control beef infusion peptone 

 medium. 



In order to test the comparative viability of the organisms on 

 the two media, the above mentioned growths (fourth transplants) 

 were kept at 16° and subcultures made at different intervals to 

 beef infusion and beef extract peptone agar. 



Stains made at the end of twenty-four days showed that all 



