586 PATHOGENIC BACTERIA. 



able in length in artificial cultures than in the blood of 

 animals and of man. The bacilli occur singly, in pairs, 

 in clumps, and sometimes in short chains. When united, 

 an angle is often formed. 



The bacillus is non-motile in both the ordinary hanging- 

 drops and in anaerobic culture. No mention is made of 

 the presence of flagella. 



The organism stains well with the ordinary stains, and 

 retains the color well in Grain's method. When stained 

 with methylene blue a granular or vacuolated appearance 



Fig. 137. — Bacillus aerogenes capsulatus (from photograph by Prof. Simon 



Flexner). 



is sometimes observable, due to the presence of unstained 

 dots in the protoplasm. 



Usually in the body-fluids and often in cultures the ba- 

 cilli are surrounded by distinct capsules — clear, unstained 

 zones. To demonstrate this capsule to the best advan- 

 tage, Welch and Nuttall devised the following special 

 stain: a cover is thinly spread with the bacilli, dried, and 

 fixed without over-heating. Upon the surface prepared, 

 glacial acetic acid is dropped for a few moments, then al- 

 lowed to drain off, and at once replaced by a strong aque- 

 ous solution of gentian violet, which is poured off and 

 renewed several times until the acid has been replaced by 



