THE BACILLUS OF TYPHOID FEVER. 439 
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 
agar, 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, 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 faeces 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- ®»dominalis; stick culture 
: in nutrient gelatin, eighth 
perature in three or four days, the surface of aay at 16°-20° C. (Baum- 
the potato has a moist, shining appearance, garten.) 
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 
