148 



and tho bacterial slime reacted immediately and distinctly alkaline to 

 neutral litmus paper. In the other tube the color was bright yellow 

 (gaml)og'e). the lead paper Avas feebly browned (only about one-tenth 

 as much as in the preceding), the substratum was very feebly grayed, 

 and the bacterial slime reactinl ditlertMitly to tln^ jieuti-al litmus ])aper — 

 i. e.. it was exactly neutral. 



J^s. 2>]nisrtt1'i cultivated on yellow and white turnips made a good 

 growth, but no brown pigment was observed. On turnip-rooted rad- 

 ishes the growth was also good and thei-e was no brown stain for a 

 month, but after that a slight >tain appeared. 



NATURK OF THK CF.T.L WALL. 



The bacterial cell wall of Ps. liyac'tntlii stains yellow with iodine 

 potassium iodide, and remains yellow on the addition of sulphuric acid 

 (Russow's cellulose test). Tests were made with germs gi-own on agar, 

 potato, starch jelly, etc. 



The bacterial slime from cultures on banana and sweet potato reacts 

 blue with Russow's test. At tirst this was supposed to indicate cellu- 

 lose in the bacterial wall. Subsequently it was discovered that the 

 blue reaction is due to some substance which may be washed away in 

 water, the bacterial masses then giving onlv a vellow stain. This sub- 

 Stance, which reacts blue, is believed to form no part of the bacterial 

 cell, but to be the dissolved substances of the substratum, carried up 

 and held between the bacterial cells by capillarity. These experiments 

 were repeated a year later with banana, using old cultures which bore 

 a thick, dull yellow slime. This slime gave no blue reaction with 

 iodine potassium iodide (absence of starch), but a very decided l)lueoii 

 adding sulphuric acid. Several washings in water greatly reduced the 

 tendency to this blue reaction, but did not entirely prevent it. This 

 was believed to be due to the fact that the water had not penetrated 

 into the center of all the l)acterial masses. The experiment was there- 

 fore repeated as follows: Masses of the surface slime aggregating 30 

 or 40 cubic millimeters, entirely free from fragments of the substratum 

 (which contained undestroyed starch), were shaken in a beaker with 

 150 c. c. of distilled water, and then put under an air pump for one- 

 half hour, so as to remove air from the slime and permit penetration 

 of the water into all parts. This water was then poured otf. more 

 added, and the exhaustion repeated. This second water was also 

 poured oti'. more added, and the beaker again pur under the air pump. 

 After the third exhaustion there remained several hundred small bac- 

 terial fragments (zoogk:ea?). As much as possible of the water stand- 

 ing over them was then poured oH' and 4 c. c. of iodine potassium 

 iodide was poured into the beaker and allowed to act for '20 minutes, 

 during which time all of the fragments became yellow. To this fluid 

 was then added 4 c. c. of the c. p. sulphuric. acid water (2:1). In an 



