1886.] NATDRAL SCIENCES OE PHILADELPHIA. 333 



of the culture. The substance of the pellicle consists of a color- 

 less matrix uniformly filled with motionless bacteria, and against 

 this the zoogloea are sharply defined. They are often brought out 

 yet more distinctly by being surrounded by a colorless layer, free 

 of bacteria, which is doubtless an extension of the ground sub- 

 stance of the zoogloea mass (fig. 4). 



The masses are far more dense than the pellicle, and are com- 

 pactly filled with refractive bacteria. They possess a definite 

 outline, and are recognizable when verj'^ small ; and although 

 they may reach 80 to 40 // long by 20 to 80 p. wide, they rarely 

 lose their distinctness. When below 10 , in length, their usual 

 form is oblong, varying to globular. They occur singly, or united 

 more or less intimately end to end in pairs, and sometimes several 

 form a short chain. At this stage they possess a uniformly even 

 and unbroken surface, which now becomes uneven and wrinkled, 

 and is finall}^ thrown into folds, giving some resemblance to the 

 external aspect of the brain. Zoogloea more than 20 ij. in length 

 have the folds of somewhat unequal height, and the sinuses deeper, 

 giving a stronger cerebric look, or when the folds are small and 

 circular, they are better described as mulberry-like. The elon- 

 gated forms, which at some stage of growth might doubtless have 

 been composed of two or more distinct masses, often take on a 

 vermiform appearance. But whatever the variations may be, the 

 distinctness of outline, the general form, and the cerebric surface 

 are unfailing characters, which so far as my knowledge extends, 

 are not found in any other species of bacteria. 



Cultivation in Fluid Media. The range of substances which 

 may serve as culture media for this organism is very wide. An 

 infusion of almost any vegetable substance containing a fair 

 amount of soluble carbohj'drates is likely to be sufficient to enable 

 growth to take place, even if not ver}'^ luxuriantly. 



The substance which on the whole has proved most satisfactor}'' 

 is an infusion of potato. This is prepared by paring a potato and 

 slicing it into three or four times its bulk of water. This is kept for a 

 couple of hours at about 70 C, by placing it over a water-bath, 

 during which time it is occasionally stirred. It is then filtered, 

 and is ready to be placed in the culture vessels for sterilizing and 

 use. If the heat is allowed to rise much above 70, the starch is 

 gelatinized, and it is only with diflficulty that the solution can be 

 filtered. The resulting liquid is clear and watery, but is often 



