Sessional_Paper_1905 — Page 430

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With regard to question II-In the paper by Mr. HANKIN named above he suggests the possibility that the true "nidus" of the plague infection is some species of flea in which the microbe causes a slowly developing infection that at length renders the insect capable of transmitting the disease, and in which insect the virus can retain or regain its virulence.

In support of this suggestion Mr. HANKIN states that he found that an epidemic of plague came to an end at the time when fleas could no longer be collected, and further quotes a similar experience published by TIDSWELL of the Sydney outbreak of 1902.

I have no accurate information as regards Hongkong on the prevalence of fleas, but since reading Mr. HANGIN'S paper I have made frequent enquiries of the people as to when fleas become most prevalent. From what I can gather these insects become most prevalent in the spring and early summer.

The larval insect lives in dry surroundings such as the dust in corners of domestic buildings and in clothing.

In about one week (or longer in cold weather) the eggs, which the adult insect lays about the house, are hatched and in about three weeks more the larva passes through the chrysalis stage to the perfect insect.

The question naturally arises-have the seasonal changes anything to do with the prevalence of fleas, and if su to what extent, and further have the seasonal habits of the people in Hongkong anything to do with increasing the possibility of plague infection being transmitted by fleas at any special time of the year?

Accurate information as to the habits of these insects in Hongkong would do much to throw light on this important question.

Whatever may be the factors which cause the start of each seasonal epidemic, experience in Hongkong has shewn that the worst epidemic period is that in which the temperature varies from about 70 to 80 degrees Fahrenheit and that with a rise to 81 degrees and over the epidemic declines.

This period of warm weather is also the period of high relative humidity and of most rainfall.

Channels of Infection in Plague.

In dealing with epidemic disease it is necessary, before empiricism. can give place to rational prophylaxis or prevention of disease on the large scale, that a clear idea be obtained amongst other knowledge of the channels of infection.

Much has already been said on this matter in respect of plague, and different workers have held and do bold different opinions on the subject.

The three theories on the way by which the causal agent of plague may gain entrance into the boly, namely, (1) through the skin, (2) through the alimentary canal, (3) through the respiratory tract, have their several supporters who base their opinions upon their own observations and upon the published records of

others.

While recognising that each recorder has grounds on which to base his theory as to the chief mode of infection in plague, I cannot accept some of his deductions in their entirety.

I propose therefore here to briefly review the present position of this so im- portant a matter.

Infection through the Skin System.

The great frequency with which palpable glandular enlargements occur in patients suffering from plague when considered in connection with the anatomy and physiology of the lymphatic system has naturally given rise to the theory that infection mostly occurs through the skin. This received strong support froin the researches of the Indian Plague Commission who have recorded the coincidence that the areas of skin drained by the glands of the neck axilla and groin vary alm st directly as the prevalence of buboes in these regions.

The important discovery justified the hypothesis that the skin is the usual place of entrance of the bacillus.