216 IMPORTANT VARIETIES OF FISSION- FUNGI. 



the colonies on glycerin-agar (13, vii b) and ascites-agar 

 (13, VII c) are less transparent and darker in color. 



The delicate, tiny, drop-like colonies which occur when 

 cultures are made direct from pest material (13, ii), when 

 magnified sixty times, appear less crumbly, sometimes 

 homogeneous, almost smooth-bordered, and elevated like 

 the head of a pin. Here, as in the colonies in gelatin, the 

 older colonies present a ver\^ delicate, transparent, finely 

 punctated peripheral zone, upon which the colony proper 

 appears built up as a hemisphere (18, vi). Young colo- 

 nies are gray ; old ones, grayish-yellow to brownish- 

 gray. 



Agar Stab. — Difficult to differentiate from the colon 

 bacterium. The surface growth is somewhat whiter than 

 with the colon. Stab is uncharacteristic and thread-like. 



Agar Streak. — The growth upon the surface from fresh 

 pest material consists of tiny, delicate, transparent, drop- 

 like colonies, which lie close to each other and appear as a 

 delicate surface-layer. The minute colonies are not conflu- 

 ent and do not become much larger. The entire layer ap- 

 pears grayish-yellow (13, ii). The growth of cultures 

 which have been long under cultivation cannot be differ- 

 entiated from that of a well-developed colon culture, but 

 is perhaps a little whiter. 



Bouillon Culture. — At first is slightly turbid ; in course 

 of time a pellicle forms, which at first is delicate, and later 

 becomes denser. Very old cultures are often clear, with 

 an abundant, crumbly sediment. In sugar bouillon the 

 sediment is more marked, also the pellicle is more luxu- 

 riant. 



Milk Culture. — Growth in milk is slight ; the milk 

 is not coagulated. 



Potato Culture. — Grows slowly. Deposit is whitish 

 to whitish-yellow, faintly shining, somewhat elevated, 

 crumbly. It is sharply outlined from the potato. 



Special Nutrient Media. — Upon boiled rice, at 30°- 

 37°, there is an abundant growth in the form of a gray 

 film (Report of the German Pest Commission). 



Chemical Activities. — (a) Chromogenesis, production 

 of odoriferous and gustable substances, liquefaction of 

 gelatin, and H2S are absent. 



