TYPHOID FEVER. 167 



Spore-formation. Gaffky considered as spores certain ter- 

 minal bright, oval bodies that are said to remain unstained. These 

 bodies (polar granules) have, in accordance with subsequent in- 

 vestigations, come to be looked upon as involution-forms. At 

 any rate the bacilli that contain such bodies are not noted espe- 

 cially for their powers of resistance, as they are destroyed with 

 certainty by exposure for ten minutes to a temperature of 60 C. 

 (140 F.)- 



The typhoid-bacillus grows in the absence of oxygen, though 

 by no means so well as in its presence (facultative anaerobiosis). 

 The temperature-optimum for the typhoid-bacillus is that of the 

 body. The organism thrives well, however, at room-tempera- 

 ture. The temperature-maximum is 46 C. (114.8 F.). 



The Appearance of Typhoid-bacilli in Cultures. 

 The bacillus of typhoid fever in contrast with most other patho- 

 genic bacteria exhibits vigorous growth on slightly acid 

 nutrient media. 



On gelatin-plates deep colonies appear as small, punctate, 

 sharply circumscribed dots ; with low powers of the microscope 

 they may exhibit a brownish-yellow color and a whetstone 

 shape. Superficial colonies are much larger, and form a bluish, 

 iridescent, delicate coating, with an irregularly serrated border. 

 Only the central portion of the colony appears, with low powers 

 of the microscope, of a yellowish color, while toward the margin 

 a delicate linear network can be observed, giving rise to a leaf- 

 like appearance. The gelatin is not liquefied. 



In gelatin stab-cultures development takes place along the 

 entire line of inoculation. Superficial growth is pronounced, 

 and presents characteristics similar to those observed in superfi- 

 cial colonies on plates. 



Gelatin Streak- cultures. From the center the entire surface 

 of the gelatin is covered by a delicate, iridescent, bluish coating. 



In all gelatin-cultures a peculiar milky turbidity of the nu- 

 trient medium frequently occurs in the neighborhood of the 

 culture. 



In agar streak-cultures and in blood-serum a whitish coating 

 of inconsiderable density forms, without characteristic peculiari- 

 ties. 



The appearance of potato-cultures is of importance. In these 

 the typhoid-bacillus grows in an invisible layer, with an ap- 

 pearance as if nothing at all had developed upon the surface 

 of the potato. If, however, an attempt is made to remove 

 material with a platinum loop, it is at once found that the potato 

 is entirely covered by a layer of some kind. Microscopic ex- 

 amination confirms this observation, and discloses the presence 

 of large numbers of actively motile rods. This mode of devel- 

 opment is quite peculiar, and occurs, so far as is as yet known, 



