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They concluded that the infection was occasioned through the intact_mucous membranes. BATZAROFF (Annl. Past. Bd. 13, 1899) and BANDI (Revue d'Hyg. Bd. 21) came to a similar conclusion, but found in addition that this method of inoculation was frequently followed by a primary plague pneumonia. It is obvious that here the infection was not through the intact mucous membrane but by way of the respiratory tract to the lungs.
Again, infection of the conjunctiva is frequently followed by general plague septicemia, and post-mortem marked pathological changes are found in the gastro- intestinal tract. The stomach shows small and large hæmorrhages. A similar condition is found in the intestine. The changes found are identical with those met with after feeding with plague bacilli or plague infected tissues.
The question would appear to arise as to whether the infection really takes place through the uninjured mucous membrane or is conveyed from the conjunc- tiva and the nose to the lungs or alimentary tract. In this connection the results obtained by RÖMER, MAYER, and HIROTA (cit. by KOLLE) are of great importance. These observers admit the occurrence of plague infection, after smearing the conjunctiva with plague infected material. They found, however, that if the nasal duct be previously ligature, such an infection does not occur.
Such a result appears to offer au explanation of the exact mode of plague infection in such cases.
The post-mortem changes found after such a method of infection, are largely centered in the alimentary tract. The stomach is deeply congested. The intes- tinal canal is swollen, oedematous and, in some cases, ulcerated. The mesenteric lymphatic glands are also swollen and oedematous, and contain large numbers of plague bacilli.
From the experimental evidence at one's disposal, the effect of smearing the mucous membranes of the conjunctiva and the nose with plague material is to produce plague infection per os. The causal agents reach the mouth or throat, and either set up the pneumonic manifestation of the disease, or pass by the œsophagus to the gastro-intestinal tract, eventually giving rise to a typical sep- ticæmic plague.
(f.) By Feeding. This method of infection would appear to be the commonest for the rat. The type of the disease is septicemic. The condition of the gastro- intestinal tract is similar to that found after smearing the uninjured mucous membranes of the nose and conjunctiva. The question of feeding and the origin of plague in the alimentary tract have been so frequently mentioned in this research, that one has little or no further comments to make in regard to the subject.
General Conclusions regarding Artificially Induced Rat Plague.
(1.) Plague in rats is either acute, chronic, or latent.
(2.) Septicæmic plague is the most characteristic type of the disease. (3.) Bubonic swellings are not marked features of rat plague.
(4.) Gastro-intestinal inoculation gives constant results.
(2.) Spontaneous Infection or the Naturally Induced Disease.-Natural infec-
tion through the skin would not appear to be common.
The effects of one infected
rat biting a healthy rat, scratching, and wounds produced by fighting, etc., are not of great importance in regard to the spread of the rat epizootic.
The part played by fleas would appear to be over-estimated. (Vide "Insects and the Spread of Plague.")
The infection per os would appear to be the most frequent mode of dissemina- tion of plague amongst rats.
The opinions expressed by different observers, in regard to infection per os, are of a conflicting nature. GIBSON, HANKIN and SIMOND in India obtained inconstant results with feeding experiments. Their observations are more or less isolated.
The majority of recent experiments goes to show that plague infection per os is the all important mode of contraction of the disease in the rat.