146 PATHOGENIC BACTERIA, 
be added to a bouillon culture of actively motile 
typhoid bacilli, the bacilli lose their motility and 
Fic. 80.—Bacillus typhosus: superficial colony two days 
old on a gelatin plate; x 20 (Heim). 
Fic. 81.—Bacillus coli: superficial colony two days old, 
on a gelatin plate; x 21 (Heim). 
soon aggregate in clumps. Dilutions of serum 
1;10 and 1:30 with a half-hour time-limit are 
