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It is possible to produce plague in all species of rats by subcutaneous in- oculation.

(b.) By Cutaneous Inoculation-i.e., by rubbing the plague virus into the skin. This method of reproducing the disease in the rat or other small animals was strongly advocated by the members of the Austrian Plague Commission. abdomen of the animal to be inoculated, is shaved, and the plague infected material is rubbed into the bare skin.

The

This method is one of great value for purposes of diagnosis. It is very useful if applied in the case of mixtures supposed to contain plague bacilli such as the faces, food, clothing, etc. For such purposes. I have found it of great use in determining my results already detailed under the heading of Human Plague. The isolation of plague bacilli from such material as fœces, etc., is a matter of the greatest difficulty. In fact, in many cases, our ordinary cultural methods would fail to give us a positive result. n resorting to the experimental method direct, namely, the cutaneous incorporation of the supposed virus, the results are found to give great satisfaction.

The cutaneous method of inoculation of the rat would not appear to give so constaut results as in the case of the Guinea pig. The method of cutaneous inoculation of plague, has been interpreted as a good instance of the passage of the B. pestis or even of any micro-organism--through the unbroken skin. On careful consideration of all the circumstances present, however, such a conclusion is by no means warranted. During the process of shaving, no matter how carefully the procedure is carried out, small breaches of the continuity of the skin are bound to be made. They may occasion no hemorrhage, and even be microscopic, yet these wounds are of sufficient magnitude to permit the passage of an organism like the B. pestis. The reason why rats are not so susceptible to this mode of infection is by no means clear, nor are the negative experimental results of KOLLE explainable. The skin of the Guinea pig is more delicate, and easily wounded than that of the rat, and again the question of expert shaving is a factor not to be forgotten in performing such an experiment.

(c.) By Intra-Peritoneal Inoculation. Little of interest from the point of view of dissemination of plague, is attached to this method of plague infection.

It has been noted that for success with this method of incorporation, small doses of the virus must be employed.

Again the plague bacilli found in the peritoneal exudate show marked capsular formation.

According to KOSSEL and OVERBACK (Arb. Kais. Ges-Amt. Bd. 18, 1901) little change is found in the peritoneum after such an inoculation of plague bacilli.

(d.) By Inhalation.-Rats are very susceptible to this mode of infection when artificially induced. The most satisfactory experiments in regard to this question are those conducted by MARTINT (Zeit. f. Hyg. Bd. 38, 1901). This investigator found that rats by inhalation of virulent plague bacilli, contract a primary plague pneumonia.

The passage of the organism by inhalation from one rat to another, would appear to be the most satisfactory method of raising the virulence of the B. pestis. This would also appear to be the case in regard to the history of pneumonic plague in man, and would account for the rapid spread of this deadly form of the disease. Of great interest in regard to the pathology of the disease, is the statement made by MARTINI, that plague bacilli isolated from such pneumonic case, gradually acquire the power of producing fatal lung plague when incorporated subcuta- neously or intra-peritoneally.

(e.) By Contact with Uninjured Mucous Membranes, e.g., the nose, conjunctiva, etc.- The members of the German Plague Commission were the first to show that by smearing plague infected material on the mucous membranes of the conjunctiva and the nose of the rat, general plague infection could be induced, They mention the occurrence of bubonic swellings in the neck and great enlargement of the spleen as results of such a method of inoculation.