360 THE ALCALIGENES— DYSENTERY— TYPHOID GROUP 
quently agglutinates either with Shiga or Flexner bacilH. The agglu- 
tination reaction, therefore, is not conclusive for clinical diagnosis 
unless a negative reaction is obtained early in the disease followed by 
a positive reaction on or after the seventh to the tenth day. 
(6) Isolation of Dysentery Bacilli from the Feces.— Dysentery bacilli 
do not invade the blood stream as a rule, and they are not found 
in the urine. The bacteriological diagnosis, therefore, depends upon 
the isolation of the organisms from the feces and their identification by 
cultural and serological reactions. 
A bit of blood-stained mucus offers the best material for isolation 
of the organisms: It should be washed tw^o or three times in sterile 
salt solution to remove extraneous organisms as far as possible, for 
experience has shown that dysentery bacilli are frequently enclosed 
in mucus. The mucus is then macerated in sterile broth, and if 
possible incubated for one or two hours at 37° C. It is then spread 
upon the surface of lactose agar plates, using the Andrade indicator, 
and incubated for eighteen to twenty-four hours at 37° C. The 
colonies are precisely similar to those of typhoid and paratyphoid 
bacilli; the final identification of the dysentery bacilli is made by their 
cultural reactions (see page 353) and by agglutination with specific 
sera of high potency. The rapifl method of isolating and identifying 
typhoid bacilli described on page 373 is equally applicable to dysentery 
bacilli. The possibility of carriers should be borne in mind when 
mild and atypical cases are under consideration. 
Dissemination and Prophylaxis. —Dysentery bacilli appear to be 
widely distributed in certain areas of the temperate zone, and out- 
breaks occur at varying intervals. Interepidemic years are occa- 
sionally characterized by considerable numbers of atypical, mild cases 
and carriers are not uncommon.^ Shiga bacillus carriers not infre- 
quently become semi-invalids, unfit for hard work. The excretion 
of bacilli is usually less intermittent than is the case with Flexner 
bacillus carriers.- 
The organisms enter the body through the mouth and intestinal 
tract, and leave it in the feces; consequently the method of trans- 
mission of the disease is similar to that of typhoid and other excre- 
mentitious disorders. There is some evidence that the disease may 
be milk-borne; exclusively breast-fed infants are rarely or never 
infected; bottle-fed babies of the same age may be infected in rela- 
tively large numbers during years which exhibit an epidemic tendency 
of bacillary dysentery. Zinsser^ has produced evidence in favor of 
the occasional milk transmission. The organism may also reach the 
body by direct transmission through carriers, in hospitals and through 
contaminated water and food. Flies may also play a part in the spread 
of the disease. 
> Kendall: Boston Med. and Surg. Jour., 1913, 169, 749; ibid., May 20, 1915. 
2 Medical Research Committee Bulletin, No. 29, 1919. 
3 Proc. New York Path. Soc, 1907. 
