5 88 



PATHOGENIC BACTERIA. 



place slowly unless such tubes are placed in a Buchner's 

 jar. The deeper colonies are the 

 largest. Sometimes the growth only 

 takes place within 10-12 mm. of the 

 surface, at others within 3-4 cm. of 

 it. After repeated cultivation the 

 organism seems to become somewhat 

 accustomed to the presence of oxy- 

 gen, and will grow higher up in the 

 tube than when freshly secured from 

 animal tissue (see Fig. 138). 



The colonies seen in the culture- 

 media are grayish-white or brownish- 

 white by transmitted light, and some- 

 times 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 subse- 

 quently attain a diameter of 2-3 mm. 

 or more. Their first appearance is 

 as little spheres or ovals, more or less 

 flattened, with rather irregular con- 

 tours, due to the presence of small 

 projecting 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-separated colonies may attain a 

 large size and be surrounded by pro- 

 jections, either in the form of little 

 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 



Fig. 138. — Bacillus 

 aerogenes capsulatus, 

 with gas-production (from 

 photograph by Prof. Si- 

 mon Flexner). 



