The Flea

e is an infectious fever caused by a specific bacterial organism. Bacillus pestis was first identified in 1894 by Kitasato, a Japanese, and immediately afterwards, but in

ed. Little is known of its toxic action, but a weak toxin has been got from cultures. The bacillus itself is

ed by the disease. In pneumonic cases the bacillus may be found in the sputum of the patient. It is the custom to speak of (a) bubonic plague, (b) septic?mic plague, (c) pneu

li are scarcely ever found in the blood in bubonic cases that the invaders are stopped by the lymphatic glands next above the point of inoculation. In such cases

een transferred to mice, rabbits, guinea-pigs, squirrels, pigs, sheep, goats, cattle and horses. Men and monkeys are equally susceptible. Cats an

res will remember the Book of I Samuel vi. 4: "Then said they, What shall be the trespass offering which we shall return to him? They answered, Five gold

Agra (1618) mentions the unusual mortality of the rats. In India it seems long to have been a custom, dictated by experience and caution, to leave houses when rats began to die. In Europe,

before the reign of the Emperor Justinian. When it raged for the first time at Constantinople (A.D. 542) the mo

th again ravaged Europe. Again the mortality was enormous. Millions perished little suspecting that fleas could be con

ed by skilful French physicians. Some of the French medical school went so far as to deny contagion altogether. The modern view is that aerial infection may

he autumn of 1896, when plague broke out in India, the men of science, who made careful observations on the spot, were struck by the

btained fleas from plague-sick rats. These he crushed, and injected the liquid into a couple of mice. One of these died of plague in three days. The German Plague Comm

idence tending to show that infected fleas could transmit infection by biting. But Simond was not able to bring forward conclusive proof. He pointed out a line of research to others which has proved exceedingly fruitful. In the same year (1898) Hankin suggested that some biting

countless rats. Numberless fleas have been collected and dissected. But this summary would be very incomplete if it did not mention the work of Verjbitski, a Russian doctor at Cronstadt, whose labours remained almost unnoticed although he made his experiments as long ago as 1902-1903. His thesis, written in Russian, was not published in any scientific journal. But his

ndia and sub-tropical countries Xenopsylla cheopis. This last species has acqui

present the plague could be transferred from rat to rat, kept in proximity, but carefully screened so as to avoid any possibility of contact. Next, fleas were collected from rats dead or dying of septic?mic plague and transferred to healthy rats living in flea-

th would be almost certain to imbibe at least some plague bacilli. There is, moreover, good evidence for believing that multiplication of the plague bacilli may take place in the flea's stomach. Nor does the blood imbibed by the flea cease to be infective when it passes from the stomach. Both the contents of the rectum and the excrements of fleas taken from plague rats often contain abundant and actively virulent plague bacilli. A number of inf

ary canal. On rare occasions it is found in the gullet when fleas have been killed immediately after feedi

leas taken from plague-infected rats remain infective: that is to say, are capable of transmitting the infection to healthy animals. Two series of careful experiments, made during the epidemic plague season in Indi

e male and the female oriental rat (

stions of all: namely, the method by which the

tance, even if it may sometimes occur. Experiments in feeding have shown that an animal is unlikely to become infected by swallowing material containing plague bacilli, unless the amount is considerable. Moreover we know that infected fleas confined in test-tube

de surface of the flea's proboscis must become contaminated, when it sucks the blood of a plague-stricken rat; but it is difficult to suppose tha

der will remember that when a flea sucks, a stream of saliva is pumped down the mandibles into the puncture. But this hypothesis is shattered by th

ply) are regurgitated and transferred to the wound by the mouth-parts, is rendered less credible when we remember th

e present in abundance in the f?ces of fleas taken from plague-sick rats, and that such f?ces are infective to guinea-pigs both by cutaneous and by subcutaneous inoculation. Experiments were made to discover whether the pricks made by fleas were of sufficient size to allow plague bacilli to enter the body, no other damage to the skin being done. Healthy fleas, confined i

ead on the skin, and, afterwards, healthy fleas were allowed to feed on

e by a flea will allow the bacillus to gain access to an animal's body and to inf

ties are not ready to express any opinion. The safest cours

them as possible. Men of science were at the same time engaged in collecting and examining the fleas from many thousands of rats. The great success of the work confirmed the soundness of the theory on which it was based. The spread of the most terrible of epidemic diseases was controlled and

st outbreak of plague in Manchuria the fleas carri

smit it as readily as the oriental rat-flea. An explanation of this was obtained when it was discovered that Pulex irritans does not live well either on rats, or on guinea-pigs, which were the subjects of the experiments. A count of the fleas was made, each day, in a number of experimental cages, in which live human fleas were placed

fleas are able to transfer infection we have little or no knowledge. But twenty-seven experiments to transmit plague from animal to anima

ss, therefore, evidently goes on. If a number of fleas be fed on a septic?mic rat and, subsequently, be kept under observation and nourished on healthy animals, the proportion found to be infected steadily diminishes day by