THE BACILLUS OF TYPHOID FEVER. 



439 



feu 



monly marked with a network of lines and furrows. Stab cultures in 

 ten-per-cent gelatin, at 18 to 20 C., at the end of three days show 

 upon the surface a whitish, semi-transparent layer, with sharply 

 defined margins and irregular outline, which has a shining, pearly 

 lustre ; and along the line of puncture a gray- 

 ish-white growth, made up of crowded colo- 

 nies, which are larger and more distinct at the 

 bottom of the line of growth. Upon nutrient 

 cigar, at a temperature of 35 to 37 C., the 

 growth is more rapid and forms a whitish, 

 semi-transparent layer. The cultures give off 

 a faint putrefactive odor. The growth upon 

 blood serum is rather scanty, in the form of 

 transparent, shining patches along the line 

 of inoculation. 



The typhoid bacillus develops abundantly 

 in milk y in which fluid it produces an acid 

 reaction ; it also grows in various vegetable in- 

 fusions and in bouillon. 



None of the above characters of growth are 

 distinctive, as certain common bacilli found 

 in normal fasces present a very similar appear- 

 ance when cultivated in the same media. 



The growth of this bacillus upon potato is 

 an important character, as was first pointed 

 out by Gaffky. In the incubating oven at the 

 end of forty-eight hours, or at the room tem- 

 perature in three or four days, the surface of 

 the potato has a moist, shining appearance, 

 but there is no visible growth such as is produced by many other bac- 

 teria upon this medium. A simple inspection would lead to the belief 

 that no growth had occurred ; but if with a platinum needle a little ma- 

 terial is scraped from any portion of the shining surface and a stained 

 preparation is made from it, numerous bacilli will be seen, some of 

 which are likely to be in the form of quite long threads, while others 

 are short and have rounded extremities. This " invisible growth " 

 has been shown by the researches of Buchner and others to be most 

 characteristic upon potatoes having a decidedly acid reaction, as is 

 usually the case. When cultivated upon potatoes having an alkaline 

 reaction a thin, visible film of a yellowish-brown color and of limited 

 extent may be developed. Inasmuch as several common and widely 

 distributed bacteria closely resemble the typhoid bacillus in form and 

 in their growth in nutrient gelatin, this character of invisible growth 



FIG. 110. Bacillus typhi 

 abdominalis ; stick culture 

 in nutrient gelatin, eighth 

 day at 16-20 C. (Baum- 

 garten.) 



