BY R. GREIG-SMITH. 



57 



The experiment seems to indicate that as the water lies in contact witii the 

 bark, tlie nutrients and tannins diffuse out and the proportion of these is such 

 that ropiuess can develop. But after a time, the tannins begin to preponderate 

 and the development of ropiness is prevented . 



Infusion "A" was treated with increasing amounts of tannic acid and seeded 

 with A2. Ropiness developed in the ccatrol, but not in the portions containing 

 _0 . 5 % and over . 



The Change in Reaction. 



During the growth in synthetic media, the bacteria prc.duce a small but 

 definite amount of acid from the sugar. In the presence of gljcerine the medium 

 may remain unaltered or it may become less acid. For example, a ropy dextrose 

 fluid showed -4-3.4° while the control was -(-1.7°. A bulk culture with glycerine 

 had at the start -\-2° to methyl red, -f5.5° to litmus and -(-8.5 to phenolphth- 

 alein . On the 6th and 12th days, when ([uite ropy, the same respective acidities 

 were determinl-d . This however is unusual, for in other cases the glycerine me- 

 dium became alkaline, as will be seen in some experiments given in the pages 

 that follow. 



The effect of varying the original acidity upon the development of ropiness 

 was tested in a few expei'iuients. 



A fluid containing glycerine, meat extract and salts was divided into 50 c.e. 

 portions, and these were given progressive quantities of phosphoric acid before 

 being seeded with the bacterium A which was probably a mixture of the phases 

 Al and A2. Ropiness appeared on the fourth day at 28° in the portions con- 

 taining originally an acidity of from -3° to methyl-red (=-(-2.5° to phenolphth- 

 alein) to -(-6° (=11.5°) but not in those containing -(-16° (=21. f°) and over. 

 The conditions were unchanged on the sixth day. 



A similar test was made with dextrose in place of glycerine . After sterilisa- 

 tion the fluid showed -9° to methyl-red and -[-6° to phenolphthalein . The por- 

 tions were acidified progressively and seeded with the mixed phases, Al and A2. 



Table iii. -Dextrose with increasing acidity. 



4-15° and over 



flocciiles 



Portions in which the phosphoric acid was replaced by sulphuric and hydro- 

 chloric acids gave similar results. 



The experiment shows that there is a certain range of original acidity from 

 about -(-5° to -(-12° as' shown by methyl-red which conditions a rapid production 



