762 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS- 



brane is possessed of great elasticity as evidenced by the post-fission movements. 

 The bacteria stain readily with aU the aniline dyes and retain the primary stain fairly 

 well by Gram's method. With Loeffler's methylene blue they stain in a character- 

 istically irregular manner, and show metachromatic "granular" forms, "barred" 

 and "solid-stained" forms (Fig. 160). On a basis of morphology and staining 

 properties, Wesbrook, Wilson and McDaniel have devised a classification which is 

 very convenient for descriptive purposes. The minimum temperature of growth 

 18° to ig°, optimum 35° to 37°, maximum 40° to 41° The bacterium grows most 

 readily in the presence of oxygen. Under certain conditions it will grow anaero- 



Oi 



Nv^ 



Fig. 160.— Wesbrook's types of Bact. diphtheria, a, c, d, granular tjrpes; a', 

 barred types; a', c^, d^, solid types. X 1500. {From McFarland.) 



c',d\ 



bically. The optimum reaction of blood serum media is about -i-o.8. The amount 

 of acid which the bacterium can endure varies with the kind of acid. Gelatin is not 

 liquefied, neither are the proteins of blood serum nor of milk. Caseinogen is not 

 changed to casein. Some carbohydrates are broken up with the production of 

 acid. AU authorities find that the bacterium forms acid from dextrose. It is 

 generally agreed that acid is produced from lactose, galactose and maltose. Action 

 on dextrin, lactose, saccharose and glycerin is variable. The majority of workers find 

 mannit is unchanged. An acid reaction in plain broth by fermentation of muscle 

 sugar may be followed by the production of alkali. . Gas is not produced under any 

 circumstances. No indol is formed. Most strains cause hasmolysis of red blood 

 cells. A true diffusible toxin is formed for the artificial production of which in 

 broth cultures peptone, absence of sugar, an alkaline reaction and free access of 

 oxygen are favorable factors. Growth on plain nutrient agar is not so abundant 

 as on Loeffler's blood serum. Colonies of two types may be found: (o) most 

 common is small grayish-white, rounded, slightly raised, almost translucent with 



