814 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



and "solid-stained" forms (Fig. 171). 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 19, 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- 



Jv* A 



, l^y vav, 



V- ^ 



<f 



(<i 



FIG. 171. Wesbrook's types of Bad. diphtheria, a, c, d, granular types; a', c', d f , 

 barred types; a 2 , c 2 , d 2 , solid types. X 1500- (From McFarland.} 



bically. The optimum reaction of blood serum media is about +0.8. 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. All 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 haemolysis 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 LoefHer's blood serum. Colonies of two types may be found: (a) most 

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

 more or less granular surface and dark center, the margins varying in irregularity, 

 and often with a thin extension spreading out from the edge; (b) less common, 

 larger, more luxuriant, white, rounded, raised, granular to nearly smooth and some- 

 what moist. Plain broth must be slightly alkaline to litmus. About one-half of 

 cultures grow readily and half very feebly. The characteristic growth is a finely 

 granular deposit at bottom and along sides of the tube leaving the broth clear; a 



