Cultivation 



345 



takes place within 10-12 mm. of the surface; at others, within 3-4 

 cm. of it. After repeated cultivation the organisms seem to become 

 accustomed to the presence of oxygen, and 

 will grow higher up in the tube than when 

 freshly isolated. 



Colonies. — The colonies seen in the cul- 

 ture-media are grayish-white or brownish- 

 white by transmitted hght, 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. Their first appearance is as 

 little spheres or ovals, more or less flattened, 

 with irregular contours, due to the presence 

 of small projecting prongs, which are quite 

 distinct under a lens. The colonies may ap- 

 pear as little irregular masses with pro- 

 jections. 



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-Uke or feathery. Their 

 appearance 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 bub- 

 bles 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 



. Fig. 117. — Bacillus 

 aerogenes capsulatus, 

 with gas production 

 (from photograph by- 

 Prof. Simon Flexner). 



