48 



Sweet Potato. 



This medium was prepared in the same wa3^ as the common potato. 



Ps. hyacinth! orew well upon it and with little, if any, retardation. 

 Usually, by the end of the first week, at 18^ to 25'^ C, the growth on 

 the aerial part was copious. This growth did not stop early, as in case 

 of the common potato, but continued for a long time, covering the 

 whole of the exposed part and filling up the water with a solid yellow 

 slime. In one set of cultures, at the end of the twent3"-second day, 

 the growth was 10 times as abundant as on the common potato, and on 

 the fift3^-sixth day 100 times as abundant. In another set of cultures, 

 made some months later, there was "much more growth than takes 

 place on the Irish potato." Usuall}^, by the end of the third week, 

 the 1 to 2 c. c. of water in the bottom of the tube was grown full of 

 the yellow slime, so as not to flow when tilted. 



The surface of this growth was wet-shining even in old cultures (55 

 days). At first the surface was smooth, but after some weeks it 

 became unev^en, i. e. , thickly set with smooth-roundish prominences, 

 which appearance I have designated as shagreen. This uneven surface 

 remained wet-shining and homogeneous in color, and I have no doubt 

 as to the purity of the culture. Even in cultures not older than one 

 week the bacterial mass did not readily dissolve or shake apart in 

 water. 



The color of Pa. hyacinthi on this substratum at the end of the first 

 week was wax-yellow to gamboge-yellow in one set of tubes and in 

 another it was '* bright-yellow." On the thirty-first da}" the slime was 

 slightly sticky and its color in mass, on white paper, was maize-yel- 

 low. Examined microscopically at this time there were no spores but 

 a great many slender chains (6 to 12 rods) mixed in with zooglcete and 

 single and paired rods. After 55 da3's the slime in one set of tubes 

 was "dull-3'ellow" and in another set "dirt3" 3'ellow," but there was 

 no distinct brown pigment. At this time, in one set of tubes, the 

 slime consisted of a mixture of long and short rods, chains, and zoo- 

 gloese. Some of the rods and chains were ver}' long, extending one- 

 sixth to one-fifth of the way across the field of the microscope (Zeiss 

 -t nun. apochromatic and 12 compensating ocular). At this time, in 

 the other set of tubes, there were numerous roundish zooglcese embed- 

 ded in the bacterial la3'er. These zoogloea? were a little whiter than 

 the body of the slime and dissolved slowl}' in water. Under the micro- 

 scope they presented the same appearance as all the zooglcBie of this 

 organism, and I had no reason to suspect contamination. 



An acid appears to be formed out of this substratum. After 31 

 da3's the slime from the bottom of a tube showed no alkaline reaction, 

 ])ut was neutral to good neutral litnuis paper. After 56 days slime 

 from the same cultures was still " neutral or slightly acid'" to litmus, 



