PLAGUE. 107 
usually somewhat straighter than those which occur 
in the stools and the “fish in stream” arrangement is 
not marked, They will not stain by Gram’s method. 
¢. The addition of a small quantity of pure strong 
sulphuric acid will give a pink or crimson tint. This is 
the “‘ cholera-red ” reaction and is caused by the action 
‘of sulphuric acid on indol in the presence of a minute 
quantity of a nitrite; many other organisms (e.g., the 
bacillus coli) produce this colour aftey the addition of 
a nitrite, very few without it. The cholera vibrio pro- 
duces nitrites as well as indol. 
INTERPRETATION OF RESULTS. 
In a case in which the above phenomena are ob- 
served, the inference that the patient is suffering from 
true Asiatic cholera is so strong that the authorities 
should be notified and the fullest precautions taken. 
A case in which they are absent is almost certainly 
not one of true cholera. 
PLAGUE. 
The bacteriological diagnosis of plague should be 
made by an expert; not because it is difficult, but be- 
cause so much hinges upon it, at least in this country. 
A brief account of the method by which a practitioner 
who was unable to obtain expert help might proceed 
may not be out of place. 
The plague bacillus is a short and rather thick rod 
which occurs in vast numbers in the bubo, in the blood, 
