MORPHOLOGY 



371 



their bacilli during the necessary manipulations will be found in every 

 preparation. 



The flagella are normally implanted regularly around the body of the 

 organism [peritrichous ] though now and again they are found arranged in 

 tufts probably from the dragging of the surround- 

 ing liquid on these highly delicate structures. 

 The bacilli are often agglutinated into clumps 

 by a matrix which stains in the same manner 

 as the flagella and it is upon this matrix that 

 the flagella appear to be implanted. 



The flagella vary in length, the average being 

 (Remy and Sugg) ; but much longer forms 

 are to be seen. They are wavy in form and 

 present three to eight undulations. 



2. Cultural characteristics. 



A. Conditionsofsrowth.-ThetyphoidbaciUus 



is a facultative aerobe. It grows on all the 



ordinary media within a wide range of temperature (4-46 C.) the optimum 



being 30-37 C. Cultures of the typhoid bacillus have no smell. 



B. Characters of growth on various media. 1. Broth. After 8-12 hours' 

 incubation at 37 C. the medium shows a slight cloudiness, which as the growth 

 progresses becomes more marked, and gives to the culture when examined 

 by transmitted light a characteristic watered-silk appearance : this may be 

 made more distinct by gently shaking the tube : later the growth becomes 

 flocculent, falls to the bottom of the tube, and forms a very abundant sedi- 

 ment. Ultimately the liquid becomes clear and develops a brownish colour. 



2. Gelatin. The typhoid bacillus does not liquefy gelatin. 

 Stab culture. At 20 C. growth along the line of the stab commences as 

 early as the second day in the form of small, round, yellowish-white confluent 

 colonies, while on the surface a thin, transparent, rather spread-out disc 

 with iridescent margins appears ; occasionally the surface growth is repre- 

 sented by a thick opaque spot of 

 very limited extent. Growth is always 

 scanty. 



Stroke culture. On the surface 

 along the line of sowing the growth 

 forms a thin transparent film with 

 irregular margins and shot with iri- 

 descent colours ; it always remains 

 scanty and ceases to increase after 

 the first week. Such is the usual 

 appearance, but sometimes a narrow, 

 thick, opaque, yellowish- white band 

 develops along the stroke. 



In the substance of the gelatin 

 long arborescent crystals are some- 

 times seen. These are due to the 

 precipitation of phosphates. 



Single colonies. Isolated colonies 

 on gelatin usually but not invariably 

 present a characteristic appearance. After incubating at 20 C. for 48 hours, 

 small circular colonies appear and soon reach the size of a pin's head and 

 later that of a lentil, but always remain thin, bluish in colour, pearly and 



FIG. 218. Typhoid bacillus. Photograph of a colony 

 growing in plate culture (6 days), x 60. 



