474 PATHOGENIC BACTERIA. 



times, composed solely of threads. The fringing threads 

 generally grow out nearly at right angles to the periphery 

 of the colony. 



The colonies of the colon bacillus are, on the average, 

 larger than those of the typhoid bacillus; they are spher- 

 ical or of a whetstone form, and by transmitted light are 

 darker, more opaque, and less refractive than the typhoid 

 colonies. By reflected light, to the unaided eye they are 

 pale yellow. The surface-colonies are large, round, irreg- 

 ularly spreading, and are brown or yellowish-brown in 

 color. Hiss claims that by the use of these reagents the 

 typhoid bacillus can be readily detected in typhoid stools. 



Piorkowski 1 recommends a culture-medium composed 

 of urine, two days old, to which 0.5 per cent, of peptone 

 and 3.3 per cent, of gelatin have been added. When 

 grown upon this medium, the colonies of the typhoid 

 bacillus appear radiated and filamentous, those of the 

 colon bacillus round, yellowish, and sharply defined at 

 the edges. The cultures should be kept at 22° C, and 

 the colonies should appear in twenty-four hours. 



When transferred to gelatin puncture-cultures the ba- 

 cilli develop along the entire track of the wire, with the 

 formation of minute confluent spherical colonies. A 

 small thin whitish layer develops upon the surface near 

 the center. The gelatin is not liquefied, but sometimes 

 is slightly clouded in the neighborhood of the growth. 

 The growth upon the surface of obliquely solidified gela- 

 tin, agar-agar, or blood-serum is not very luxuriant. It 

 forms a thin, moist, shining, translucent band with 

 smooth edges. 



When a potato is inoculated and stood in the incubat- 

 ing-oven, no growth can be detected at the end of the 

 second day, unless the observer be skilled and the exam- 

 ination thorough. If, however, the medium be touched 

 with a platinum wire, it is discovered that its entire sur- 

 face is covered with a rather thick, invisible layer of a 

 sticky vegetation which the microscope shows to be made 



1 Berliner klin. Wochenschrift, Feb. 13, 1899. 



