Cultivation 



335 



accustomed to the presence of oxygen, and will grow higher up in 

 the tube than when freshly isolated. 



Colonies. — The colonies seen in the culture-media are grayish- 

 white or brownish-white by transmitted 

 light, and sometimes exhibit a central dark 

 dot. At the end of twenty-four hours the 

 larger colonies do not exceed 0.5-1.0 mm. in 

 diameter, though they may subsequently 

 attain a diameter of 2-3 mm. or more. 

 Then first appearance is as little spheres or 

 ovals, more or less flattened, with irregular 

 contours, due to the presence of small pro- 

 jecting prongs, which are quite distinct under 

 a lens. The colonies may appear as little 

 irregular masses with projections. 



After several days or weeks, single, well- 

 shaped colonies may attain a large size and 

 be surrounded by projections, either in the 

 form of Uttle knobs or spikes or of fine 

 branchings — hair-like or feathery. Their ap- 

 pearance has been compared to thistle-balls 

 or powder-puffs and to thorn-apples. When 

 the growth takes place in the puncture, the 

 feathery projections are continuous. Bubbles 

 of gas make their appearance in plain agar as 

 well as in sugar-agar, though, of course, less 

 plentifully. They first appear in the line of 

 growth; afterward throughout the agar, often 

 at a distance from the actual growth. Any 

 fluid collecting about the bubbles or at the 

 surface of the agar-agar may be turbid from 

 the presence of bacilli. The gas-production 

 is more abundant at 37°C. than at the room 

 temperature. 



The agar-agar is not liquefied by the growth 

 of the bacillus, but is often broken up into 

 fragments and forced into the upper part of 

 the tube by the excessive gas-production. 



Bouillon. — In bouillon, growth does not 

 occur in tubes exposed to the air, but when 

 the tubes are placed in Buchner's jars, or 

 kept under anaerobic conditions, it occurs 

 with abundant gas-formation, especially in 

 glucose-bouillon, and the formation of a 

 frothy layer on the surface. The growth is rapid in development, 

 the bouillon becoming clouded in two to three hours. After a few 



Fig. 120. — Bacillus 

 aerogenes capsulatus, 

 with gas production 

 (from photograph by- 

 Prof. Simon Flexner). 



