10 



but in no way restrained. The importance of this fact will be apparent 

 a little later when we come to discuss the effect of acid broths. 



On the fourth da}", in this alkaline beef broth, Ps. liyaclntln showed 

 a small amount of yellow precipitate. On the 6th day there was less 

 precipitate than in tubes of acid beef broth (stock 286a) 11 days old, 

 but it was yellower. The clouding was so slight that a penholder was 

 easily visible behind a thickness of two tubes. 



On the eleventh or twelfth day there was more of the yellow pre- 

 cipitate than on the sixth, but it was not copious. Rolling clouds were 

 visible on shaking, but no zoogloeBe, There was no pellicle, but now 

 for the tirst time a feeble rim of germs was lo be seen on the wall of 

 the tube at the surface of the fluid. Under a Zeiss hand lens (X 6 

 aplanat) this rim appeared as a pale amorphous membrane thickly set 

 with a series of roundish colonj^-like aggregates, which were white or 

 yellowish, and which did not dissolve when shaken down into the fluid. 

 Four days later the largest of these colony-like bodies were distinctly 

 yellow, the smaller ones being white. On the twentieth da}" the fluid 

 was uniformly clouded; there was no pellicle, pnd no ragged zoogloeas 

 were visible to the naked e3'e. The bright yellow precipitate on the 

 bottom of the tube now covered a diameter of only 1 mm. The rim 

 of germs was broad and iilmy. It easily jarred off in large fragments, 

 or as a whole, and fell to the bottom. It contained a great many 

 zoogloeaB set at regular intervals in what still looked under a X 6 Zeiss 

 aplanat like a homogeneous membrane. The upper, larger, and older 

 aggregates were decidedly yellow, and set so closely as to form a yellow 

 border on the upper rim of tbe ring, which was exposed to the air. The 

 lower, smaller, and younger zoogkea? on this ring were white, this 

 part being submerged or bareh" out of the fluid. [Subsequent observa- 

 tions showed that these white zoogloea? always became yellow with 

 increasing age and size.] The greater part of the clouding was still 

 attributable to individual germs, but some small zoogloeas could now 

 be seen in it, especially when examined with the hand lens. Under 

 the compound microscope (Zeiss 16 mm. and 12 comp. oc.) the zoogloeee 

 on the rim looked like small, closely set colonies on an agar plate, i. e. , 

 they consisted of roundish, colony -like bodies on a paler, homogeneous 

 looking membrane. Stained with gentian violet and examined under 

 high powers the homogeneous substratum was seen to be composed of 

 slender rods, which were often in short chains of 6 to 12 or more seg- 

 ments, the individuals forming the chains being distinct and of the 

 same size and shape as those not joined. 



On the thirty-third day there was a moderately abundant yellow 

 precipitate, and the color approximated Ridgway's canary yellow. 

 The fluid was less cloudy than it had been, but was still uniformly so. 

 It was not turbid with zoogloeee, but some small flecks were floating in 

 it. There was no pellicle, but an easily detached, pale, fragile, homo- 

 geneous rim of germs, which was closely set with small, roundish, uni- 



