446 THE BACILLUS OF TYPHOID FEVER. 
the bacilli of the colon group multiply in it and cause the me- 
dium to become clouded within twenty-four hours. Abel (1894), asa 
result of extended experiments, arrives at the conclusion that the 
formalin test cannot be relied upon for distinguishing the typhoid 
bacillus from certain similar bacilli, which also fail to grow in for- 
malin solution. But, on the other hand, a bacillus which grows in 
bouillon containing 1:7,000 of formalin can be definitely pronounced 
to be not the typhoid bacillus. 
Elsner (1895) recommends the following method for the detection 
of the typhoid bacillus in water or in feeces: To potato gelatin, pre- 
pared by the method of Holz, he added one per cent of potassium 
iodide. But few species of bacteria will grow in this medium, but 
Bacillus coli communis grows in it luxuriantly, forming fully de- 
veloped colonies at the end of twenty-four hours. The typhoid col- 
onies, on the contrary, are only just visible under a low power at the 
end of twenty-four hours, and at the end of forty-eight hours are 
seen as small, shining, drop-like, very finely granular colonies. At 
the same time the colonies of the colon bacillus are much larger, 
coarsely granular, and of a brownish color. By this method Elsner 
succeeded in obtaining pure cultures of the typhoid bacillus from 
the feeces in fifteen out of seventeen cases of typhoid fever, in various 
stages of the disease. Lazarus (1895) has tested this method and re- 
ports that he succeeded without any difficulty in obtaining pure cul- 
tures of the typhoid bacillus from the alvine discharges of typhoid 
patients. 
When the typhoid bacillus and the colon bacillus are planted to- 
gether, in the same liquid medium, the first-mentioned bacillus, even 
when in excess at the outset of the experiment, soon disappears and 
the Bacillus coli communis remains in full possession. According 
to Wathelet (1895) the colon bacillus will grow in bouillon which 
has served as a culture medium for the typhoid bacillus, or on the 
surface of an agar plate from which a typhoid culture has been re- 
moved; but the typhoid bacillus fails to develop in culture media 
which have served for the development of the colon bacillus. 
The various diagnostic tests which have been proposed, and the 
extensive literature of the subject, show that the recognition of the 
typhoid bacillus in water, feeces, etc., is attended with serious diffi- 
culties. This is chiefly due to the fact that bacilli have been ob- 
tained from various sources which resemble more or less closely the 
typical typhoid bacillus as obtained from the spleen of a typhoid 
patient (or cadaver) and the “colon bacillus” as found in the alimen- 
tary canal of healthy men and animals; and also from the fact that 
the bacillus, as obtained from typhoid cases, varies to some extent in 
its biological characters, and that varieties may be produced in the 
