143 



and the bacterial slinie reacted inimediatel}' and distinct!}' alkaline to 

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

 (gamboge), the lead paper was feebly browned (only about one-tenth 

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

 and the bacterial slime reacted differently to the neutral litums paper — 

 i. e., it was exactly neutral. 



Ps. 2>haseoU cultivated on 3^ellow and white turnips made a good 

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

 ishes the growth was also good and there was no brown stain for a 

 month, but after that a slight stain appeared. 



NATURE OF THE CELL, WALL. 



The bacterial cell wall of Ps. hyacinthi stains yellow with iodine 

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

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

 potato, starch jelly, etc. 



The bacterial slime from cultures on banana and sweet potato reacts 

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

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

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

 water, the bacterial masses then giving only a yellow 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 su])stratum, 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 blue on 

 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 bacterial masses. The experiment was there- 

 fore repeated as follow^s; Masses of the surface slime aggregating 30 

 or 40 cu])ic 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 ;is to remove air from the slime and permit penetration 

 of the water into all parts. This water was then poured off', more 

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

 poured off, more added, and the beaker again put under the air pump. 

 After the third exhaustion there remained several hundi'ed small bac- 

 terial fragments (zooglo^ie). As nmch as possible of the water stand- 

 ing over them was then poured off 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. j). suli)iuiric-.acid water (2:1). In an 



