BY R. GREIG SMITH. 391 



presence of albuminoids secreted by or contained in the bacteria. 

 When the albuminoids are coagulated by treatment in the auto- 

 clave the slime is altered to a gum. 



Having indicated the method for obtaining a solution of the 

 gum acids free from dead organisms, a word may be said about 

 the bacteria. The bacterium from Acacia penninervis was 

 identical with that separated from A. binervata, but while with 

 the former another bacterium was associated, the bacteria in the 

 latter were in pure culture. The bacteria, however, were of 

 different races — indicated only by the production of larger 

 colonies on nutritive media and more slime on tannin-saccharose- 

 potato agar. The stronger race (from Acacia binervata) was used 

 subsequently for the production of the artificial gum. 



The medium upon which most slime was obtained consisted of 



Potato extract 1,000 c.c. 



Saccharose 50 grms. 



Agar 20 ,, 



Tannic acid 3 ,, 



The potatoes were washed, pared, eyed, grated and finally 

 strained and pressed in a meat-press. The juice was then allowed 

 to stand overnight in a flask of such a size that the juice filled 

 the neck. The darkening of the fluid by contact with air was 

 thus minimised. In the morning the juice was siphoned off from 

 the starch and filtered. An equal volume of water was added to 

 the filtrate, which was then boiled to coagulate the albuminoids, 

 which were removed by filtration from the potato-extract. To the 

 extract thus obtained, the sugar was added and the solution 

 heated in the autoclave to three atmospheres' pressure"^ in order to 

 kill the spores of Bac. levaniformans, which are generally present in 

 commercial sugar. After removal from the autoclave, the chopped 

 agar was added and the solution was returned to the autoclave 

 and heated to one and a half atmospheres' pressure to bring the 

 agar into solution The tannin was then added and the medium 

 was steamed for an hour, after which it was cooled to 50° and 

 poured into sterilised (by flaming) large damp-chambers or small 



* This would be unnecessary if dextrose were used. 



