226 BIOLOGICAL PROBLEMS 



It only remains to depict in a few words the per- 

 sonality of the Reading bacillus itself. Morphologi- 

 cally it is a large gram-positive organism with 

 rounded ends, which forms a large oval spore, either 

 subterminally or, less frequently, centrally, after thirty 

 to forty hours incubation at 37 C. At ordinary tem- 

 peratures growth is very slow. In broth cultures 

 chains are frequent, and beading of the individual 

 cell is sometimes visible. 



The illustration here reproduced gives some idea 

 of these characters and of the progress of spore forma- 

 tion in a young culture. 



Unfortunately morphology is very little to go by, 

 since half a dozen other organisms of quite divergent 

 properties are positively indistinguishable from our 

 organism under the microscope. 



On agar characteristic colonies are formed, with 

 a small dense nucleus and long, spreading fimbrias 

 all round. It is principally by noting these that 

 the organism may be picked out from a mixture, 

 though its great heat resistance is a help, since the 

 spores of few other anaerobes will tolerate an hour's 

 boiling. 



In meat broth there is little change before the 

 third day, when blackening first becomes appreciable. 

 Subsequently the blackening and solution of the meat 

 proceed rapidly, with the production of evil-smelling 

 gas, until the meat is about three-quarters gone. At 

 this point the products of reaction accumulate under 

 ordinary cultural conditions so as to put a stop to 

 further growth. The addition of an adsorbent will 

 prolong it somewhat, but never to complete solution 

 of the medium. After about a week proliferation 

 ceases, all the bacilli form spores and settle to the 

 bottom in a white layer, leaving the fluid clear and 

 abating the smell. The spores can be dried on cotton- 



