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The part played by air in the dissemination of infective diseases is dependent upon the vitality possessed by the causal agents of these diseases. If the exciting agent be capable of an extracorporeal or saprophytic existence, air will obtain an important place amongst the methods of spread of such an infection. On the other hand, and this is true of the majority of infectious diseases, should the pathogenic bacteria be obligately parasitic or facultatively saprophytic, the chances are against the air playing an important role in the spread of such diseases.
The latter is true of plague. The B. pestis thrives best in contact with living tissues. On reaching the external air it meets with many harmful influences. These render it innocuous or cause its death.
The possibility of the transmission of plaque infection through dust may be passed over as unimportant.
The spread of plague by so called drop infection, however, is of great im- portance. This method of conveyance of infective viri, has been the subject of thorough investigation by FLÜGGE and his pupils, and its significance as a mode of the spread of pathogenic micro-organisms has become widely recognised during the past few years.
By drop infection, we mean, the direct conveyance of infective viri from one person to another by means of microscopic particles of sputum. Such particles of sputum are widely diffused into the external air during the acts of speaking, coughing, or sneezing, etc. In this way, it is possible for plague bacilli in the sputum of plague infected individuals to be scattered broadcast into the surround- ing atmosphere, the infected particles probably being inhaled by persons in the immediate neighbourhood. It must be borne in mind that such a spread of infection does not take place at any considerable distance. Actual contact or close association with such plague patients would appear necessary in order for the occurrence of infection.
In plague, the part played by drop infection is limited almost entirely to cases of primary pneumonic plague. In this type of the disease the bacilli ejected with the sputum are said to possess high degrees of virulence. Considerable risk. therefore, is run by medical men, nurses, and attendants on such cases, especially so should they be in close association with pneumonic plague patients at a time during which any sudden respiratory effort is made.
The actual sputum itself, does not appear to possess any terrors. The col- lected sputum is of no greater danger than any of the other infected secretions or excretions.
The sputum in cases of so called secondary pneumonia in septicæmic plague, is also dangerous, but less so apparently than that ejected by patients suffering from primary pneumonic plague.
In ordinary cases of septicemic plague, with or without bubonic formations. drop infection is of no importance.
The history of plague epidemics in recent years appears to relegate to air infection in general no important part in the spread of the disease. In the accounts of plague in India we find mention made by the members of the Austrian, German, and English Commissions, etc., of the apparent immunity of attendants in plague hospitals.
MÜLLER, of the Austrian Plague Commission, states that during the epidemic in Bombay none of the attendants contracted plague. They were constantly in close contact with all types of the disease, they nursed the cases, cleansed them, removed the sputum, fœces, and other excreta, washed the clothing and bedding, yet not a single instance of plague occurred amongst them.
Again the majority of them were barefooted, and frequently had abrasions on their feet. Further, medical officers in charge of plague hospitals do not contract the disease. Again, patients presenting indefinet symptoms are frequent- ly sent to Hospital for observation. They are soon diagnosed as ordinary pneu- monia, malaria, etc., and treated accordingly. Such patients frequently have to lie in a bed alongside a pronounced case of plague. The ward may be full of other