388 THE ETIOLOGY OF TROPICAL DISEASES 



after twenty-four hours' incubation that the top layer contains 

 actively motile vibrios, which can now be isolated readily by gelatine- 

 plate culture. 



6. To demonstrate in a rapid manner the presence of cholera 

 bacilli in evacuations, even when present in small numbers, a small 

 quantity must be taken up by means of a platinum wire and placed 

 in solution containing 1 per cent, of pure peptone and "5 per cent, 

 sodium chloride (Dunham's solution). This is incubated as in the 

 case of the water, and in twelve hours is filled with a turbid growth, 

 which when examined by means of the hanging drop shows 

 characteristic bacilli. 



7. Pfeiffer's Test. — Take a loopful of six hours' agar culture of 

 suspected cholera bacilli, and add it to 1 c.c. of ordinary broth con- 

 taining '001 c.c, of anti-cholera serum (see p. 423). The mixture 

 is injected uitra-peritoneally into a guinea-pig of 250 grammes. 

 In 20-30 minutes a drop of peritoneal fluid is withdrawn and 

 examined microscopically for comma bacilli, when, if the reaction is 

 positive, it will be found that the spirilla have broken down into 

 granules, 



3. Plag-ue 



This disease, like anthrax and leprosy, has a long historical 

 record behind it. As the Black Death, it decimated the population 

 of England in the fourteenth century, and visited the country 

 again in epidemic form in the middle of the seventeenth century, 

 when it was called the Great Plague. It is highly probable that 

 these two scourges and the recent epidemic in the East are all 

 forms of one and the same disease. As a matter of fact, it is 

 difficult to be sure what was the exact pathology of a number of the 

 grievous ailments which troubled our country in the Middle Ages, 

 but from all accounts bubonic plague and true leprosy were amongst 

 them. The former came and went spasmodically, as is its habit; 

 the latter dragged through the length of several centuries. 



There are four chief varieties of plague : first, the hiibonic form, 

 the most common and typical ; the lymph glands are chiefly affected 

 in the groin, the axilla, or the neck ; secondly, the s&pticcemic form 

 in which the bacillus reaches the blood ; thirdly, the pneumonic, in 

 which the lungs are mainly affected; and fourthly, pestis minor, in 

 which the affection of the glands stops short of the septicsemic stage, 

 and even the local symptoms are slight, There are certain symptoms 

 common to all forms of plague, when at all severe. 



Symptoms of Plague.— An ordinary attack of plague usually 

 begins three to five days after exposure to infection. Such attack may 

 develop gradually, but, generally, there is sudden onset with much 

 fever, as indicated by a high temperature, rapid pulse, headache, hot 



