MICROBIAL DISEASES OF MAN AND ANIMALS. Oil 



zag chain. The arrangement is most clearly understood and remembered by consider- 

 ing the peculiar "snapping" type of fission characteristic of the group. There are 

 no flagella and no spores. The cell membrane is possessed of great elasticity as 

 evidenced by the post-fission movements. The bacteria stain readily with all the 

 aniline dyes and retain the primary stain fairly well by Gram's method. With 

 LoefHer's methylene blue they stain in a characteristically irregular manner, and show 

 metachromatic "granular" forms, "barred" and "solid-stained" forms (Fig. 105) 

 On a basis of morphology and staining properties, Wesbrook, Wilson and McDaniel have 

 devised a classification which is very convenient for descriptive purposes. The min- 

 imum temperature of growth is 18 to 19, optimum 35 to 37, maximum 40 to 41. 

 The bacterium grows most readily in the presence of oxygen. Under certain condi- 



FIG. 105. Westbrook's types of Bact. diphtherias, a, c, d, granular types; a', c', d' 

 barred types; a 2 c 2 d 2 , solid types. Xisoo. (From McFarland.) 



tions it will grow anaerobically. The optimum reaction of blood serum media is about 

 + 0.8. The amount of acid and alkali which the bacterium can endure varies with 

 the kind of acid. Gelatin is not liquefied, neither the proteins of blood serum nor 

 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 pro- 

 duction of which in broth 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: (a) most 



