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The central nervous system is congested, with occasional blood extravasations. Examined bacteriologically, almost all the organs and tissues are full of plague bacilli. The spleen is often found choked with bacilli. Large numbers are found in the urine, feces, and saliva.
In artificially inoculated animals, the tissues about the point of entry of the virus are infiltrated with B. pestis.
If the inoculation of the rat be carried out cutaneously, according to the methods advocated by the Austrian Plague Commission, the subcutaneous tissues underlying the area of inoculation, are found to be infiltrated with extravasated blood and cleruatous fluid in which plague bacilli are abundant. This method of inoculation does not give so certain results in the rat as in the Guinea pig.
It is an excellent method of demonstrating the presence of plague bacilli in fluid, such as the urine, fœces, etc. My experience with the cutaneous method of rat inoculation is in agreement with that of KOLLE (Zeit. f. Hyg. Bd. 36, 1901).
Chronic Rat Plague. This form of rat plague would appear to be more com- mon than is generally supposed. Numerous instances of this disease have been found at the Public Mortuary during the systematic examination of live and dead
rats.
In general, chronic rat plaque is more commonly found during the interval between epidemics of plague.
The question as to the relative frequency of the varieties of the rat epizootic throughout the year will be discussed later on.
At present, however, it may be said, that there exists a considerable amount of evidence in favour of the view that the epizootic is maintained from year to year through a persistence of rat plague in chronic or latent form.
Many of the live rats sent to the Public Mortuary for bacteriological exam- ination show symptoms of some chronic wasting disorder. They show little activity. They are usually emaciated. Their hair is ruffled, matted together, and frequently areas of bare skin are found. The animals eat little. There is frequently a dis- charge of mucus from the mouth, and diarrhoea of a variable degree.
By keeping such rats alive and under observation, facts of an interesting nature may be obtained.
An examination of their blood frequently shows the presence of plague bacilli.
Such animals live for an indefinite period of time. The observations of others, e. g., ROLLE and MARTINI (Dent. Med. Wochen, 1902) prove that chronic plague may exist in rats for months.
My own observations are incomplete. Owing to the want of proper accom- modation and assistance, I was unable to carry on the experiments for a period longer than a month.
It would be interesting to follow out more closely the course of chronic rat plague. I have already made arrangements to carry on further experiments in regard to the subject.
Rats suffering from chronic plague look pitiable objects of suffering. They become more and more e naciated. Chronic diarrhoea is present and occasionally skin eruptions such as papules make their appearance.
Death takes place from exhaustion or some intercurrent disorder.
During life, these animals discharge plague bacilli with their faces and urine. Post-mortem Appearances of Chronic Rat Plaque.-There is great emaciation and loss of adipose tissue. The animals may simply be skeletons within their
skins.
Congestion of the tissues is not a marked feature. The lymphatic glands are frequently found enlarged and hard. On section, areas of necrosed tissue are found. These consist of thick cheesy looking material. Plague bacilli are rarely The internal organs show small areas of
found in such areas of dead tissue. necrosis-recent or old.