13Y R. GREIG SMITH. 599 



organic acids, sucli as acetic, and I have alread}^ shown that it is 

 partly soluble in the acids excreted by the cell. An indication 

 of the diffusive action of the excreted acid is seen in the dis- 

 appearance of the gummy layer at the bottom of resting fluid 

 cultures already mentioned on page 592. 



The addition of peptone to a culture fluid, as a rule, causes a 

 numerical increase of the bacteria. If the gum is the diffluent 

 capsule, then the greater the number of bacteria the more gum 

 will probably be formed compared with the other products. As 

 an increase of peptone does increase the percentage of gum 

 actually and relatively, one is justified in concluding that the 

 most probable source of the gum is the capsule. 



On staining the cells by the night-blue method, as used for 

 demonstrating flagella, a structure similar to a capsule is 

 manifest. It is possible that the appearance might result from 

 the method of staining, but it is more than probable that the 

 structure is the capsule. 



The Chemical Nature of the Gum. 

 The gum was precipitated from peptone-saccharose culture by 

 alcohol, and dissolved in water and again precipitated. This was 

 repeated several times, and finally it was allowed to stand under 

 dilute spirit for a week. The gum was then freed from alcohol 

 and tested for reducing sugars. No reduction of Fehling's 

 solution was obtained, and the gum was, therefore, taken as 

 being practically pure. When dried it appears as a pale yellow, 

 partly transparent mass. It forms with water an opalescent 

 semi-solution, and apparently swells up rather than dissolves. 

 From the semi-solution the gum does not separate when allowed 

 to stand for lengthened periods, nor when centrifuged. It does 

 not reduce Fehling's solution, and does not form an osazone with 

 phenylhydrazine. When warmed with dilute sulphuric acid, or 

 with dilute hydrochloric acid, a sugar is produced, which reduces 

 Fehling's solution, and which forms an osazone, having the 

 solubility, appearance and melting point (205°) of glucosazone. 

 The sugar is, therefore, either dextrose, levulose, or a mixture of 

 both these suo-ars. 



