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It is evident that considerable difference of opinion exists among plague experts in regard to the communicability of the plague virus to man and the connection between epizootic and epidemic plague.
Of importance in regard to my researches are the instances of plague infection emanating from grain and food stores. (Vide "Food and its relation to Plague.")
Again, the general trend of opinion is against the hitherto advanced causes of epidemic plague, namely, direct and indirect mode of communication of the the disease, and place infection. My own experience of plague epidemics leads me to conclude that, apart from cases of primary pneumonic plague, the dangers of one person infecting another are over-estimated, and that place infection, apart from the presence of infected rats, is of no great significance.
We know that rats are highly susceptible to plague, and they readily commu-. nicate the infection to other rats. Rars when suffering from plague are peculiar in their habits. They leave their holes. They are apparently deprived of any sense of fear or danger when near human beings. They progress with a drunken like gait Conclusive movements cause them to make erratic springs into the air during ordinary progression. They die suddenly, usually from convulsions.
The natives of Bombay are so frightened by the peculiar appearance of these animals, and the finding of dead rats in their houses, that they flit at once.
According to ZUPITZA (Zeit. f. Hyg. Bd. 30, 1899) the natives of Kisiba in Central Africa have the same dread of rats either suffering from this condition or dead in their dwellings.
These remarks bring me up to the general consideration of my own results. Much evidence has been advanced in favour of the rat theory and that, when added to the conclusions drawn from my own charts, ought to bring these two outbreaks into close relationship to each other.
Coincidences between the epizootic and the epidemic on the same premises have been found on many occasions. Frequently, however, such is mixed. I have found it impossible to go into this part of the research, nainely, the determination of the incidence of rat and human plague in each individual plague infected house in Hongkong. By compiling curves of the outbreaks for each Health District of the city, it is evident that an extremely close connection exists between the outbreaks.
Time and place relations are indicated sufficiently well in the appended charts and accompanying notes. What is of great importance in regard to the whole question is that epizootic plague always precedes epidemic plague.
The possible intermediaries necessary to convey the infection to man have already been sufficiently discussed under human and rat, plague.
WILLIAM HUNTER.
The Bridging of Epidemics.
From two charts which are appended, it will be seen that epizootic plague is present throughout the whole year. In the remarks to these charts, various conclusions are drawn in regard to the connection between the outbreaks..
What we have to explain is yearly recrudescence of the epizootic and the epidemic.
So far as the epidemic is concerned, my charts appear to show that human plague is dependent on rat plague. Within 10 or 14 days after the commencement of the epizootic, human plugue appears. This is true, not only of Hongkong in general, but of each individual district in the Colony.
Therefore in dealing with this question, we have to explain the behaviour of the epizootic. Rat plague is present throughout the whole year.
It becomes epizootic at certain times of the year-in Hongkong during the first quarter of every year.
In order to explain the regular reappearance of the epizootic, we have to consider the question of the virulence of the B. pestis, and the period when rats are most prolific.