THE BACTERIOLOGICAL DIAGNOSIS OF PLAGUE* 
By C. BALFOUR STEWART, M.A., M.B.Camb. 
Thompson Yatks Laboratoriks, Univkrsity College Liverpool ; late attached to Plague 
Research Laboratory, Bombay ; Assistant Bacteriologist Liverpool Corporation ; 
Research Assistant, Pathological School, Thompson Yates Laboratories 
The following methods are those adopted at the Plague Research Laboratory for diagnosing 
plague in Man or animals, and for testing a plague culture. Naturally, in Bombay, we had to do 
with recent cultures, and the following remarks apply to such. A plague culture grown for a long 
time on artificial media does not seem to give the same results ; at any rate, a culture of plague 
which had been kept for a long time in a laboratory, and which was given me to examine, did not 
grow typically in broth. 
Media 
Only two kinds of media are used— agar and broth ; it is found impossible to work with 
gelatine on account of the high temperature. Ordinary agar slant tubes are allowed to dry. 
Should they be required for use soon after they are made it is best to place them for a few days in 
a drying bottle, with quicklime at the bottom, otherwise they may be dried by leaving them on 
their sides in a dark room for a few weeks. If plate cultures are made it is better to prepare the 
plate, and let it dry and make a smear culture. 
Broth 
A special peptone solution and infusion of meat made out of Goat's flesh is used on account 
of native religious prejudice against beef and commercial peptone, but ordinary broth made of beef 
infusion, plus i per cent, peptone plus 0.5 per cent, salt does just as well, or better. 
The broth need not be neutralized unless very acid. I have often found the plague 
bacillus grow better in broth made without any addition of alkali, the reaction to blue litmus paper 
being a slight tinge of red. As such broth generally gives a precipitate after sterilization, and 
requires to be filtered and sterilized again, it is better for practical purposes to render the broth 
slightly alkaline, the less the better, and not more than is given by 0.2 gram per cent, of caustic 
soda added to the broth after being made neutral. About 100 c.cm. should be put into globular 
flasks of about 200 c.cm. capacity, and sterilized at a slightly lower temperature tlian that at which 
the broth was originally heated ; if this is done, no further precipitate will come down. 
Source of the Plague Microbe 
The plague microbe is found in the blood shortly before a fatal termination of a case of 
plague, so the specimen should be taken sliortly before or soon after death. 
The sputum of a case of pulmonary plague contains the bacilli. If the bacillus is to be 
sought for in the bubo, it is better to make a small incision in the skin, and push a small sterilized 
glass pipette into the gland, and suck up a drop or two of the juice. Tin's should be done before 
suppuration has commenced. 
* Reprinted from the ' British Medical Journal.' 
