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Instances are known of infectious matter producing disease when energetically rubbed into the skin. The organisms, in this way, reach the sweat and sebaceous follicles and subsequently give rise to disease. Such instances, however, are rare. So far as plague is concerned, the Austrian Plague Commission made the import- ant statement that plague bacilli, when rubbed into the shaved skin of a rat or guinea pig, always occasions a lethal infection. This method has been recommend- ed as a delicate diagnostic test. In my opinion, however, this method of diagnosis loses much of its significance as an instance of skin infection, when we consider whether the shaven skin of such animals is to be regarded as unbroken, with no solution of continuity, or, what is more likely, whether the bacilli make their way through microscopic wounds, the production of which during the process of shaving being almost unavoidable. The question as to the part which the skin plays as an avenue of infection in plague, would appear from my researches to be exaggerated. That such a mode of infection does happen, no one denies. In- stances of such are frequently forthcoming. The evidence at my disposal, how- ever, is decidedly against the general conclusion, that the skin is the common portal through which the plague bacillus effects an entry into the body of man or animals. The presence of groin buboes as frequently in well booted as in bare footed individuals, the irregular distribution of such bubonic swellings, etc., are against the theory of skin infection. The bulk of evidence amassed by my re- searches is against the occurrence of such a mode of production of the disease. My experience leads me to the same conclusions as drawn by WILM, who advanced much logical proof against such a method of infection. If infection took place through the skin, avillary buboes ought to be as common as groin buboes. Again one would expect intense inflammation of the tissues at the point of inoculation similar to that found in animals. One would expect the frequent occurrence of plague in bubonic form amongst those who are employed in special plague work such as the removal of infected rats, clothing and household utensils. These and many other factors already mentioned in different sections of this research are sufficiently pronounced to cast much suspicion upon the questionable role played by the unbroken skin in nature in the production of plague.

2. The Respiratory Tract. The introduction of the plague virus, via the respi- ratory tract, is a most important mode of production of the disease. Primary pneumonic plague is produced by the so-called drop-infection of FLÜGGE.

The air cannot be regarded as dangerous. The B. pestis does not survive dessication, and possesses, so far as we know, no permanent forms, enabling it to continue its existence as a saprophyte. The plague bacillus cannot exist in the air as dust. This statement is amplified by the non-occurrence of cases of the disease amongst those in charge of plague patients or in special plague work. Had the B. pestis an aerial existence we should expect to find numerous instances of such a mode of infection amongst those in close contact with the disease. Further such a mode of dissemination would be further accelerated by the increased viru- lence possessed by such plague bacilli present in the lung tissue. (KOLLE and MARTINI, Deut. Med. Wochen, 1902.)

Close contact with the disease and direct transference of the moist particles of pestiferous sputum are necessarry for infection to take place through the respi- ratory tract. This explains the many dreadful visitations of the disease which one frequently hears of, where whole families have been exterminated in a few days. Primary pneumonic plague would not appear to be as common now-a-days as formerly. Such a form of plague differs entirely from the other varieties of the disease.

Primary pneumonic plague, where present, does not, like septicemic plague, occur broadcast over a town or city. The cases are at first localised. The disease shows a steady march, blotting out of existence whole families or congregations of people.

This form of the disease would appear to be rare in Hongkong. The varie- ties found are mostly secondary pneumonic manifestations occurring as complica- tions of ordinary septicemic plague. Details in regard to these forms of disease have already been given under the "l'ost-inortem Appearances of Plague."

3. The Digestive Tract. The intestinal canal is the starting point of a large number of acute infectious diseases. That plague should be included in the list of such diseases has been the subject of much varied discussion. The majority of