234 TKANSACTIOXS AND PROCEEDINGS OF THE [Sess. LXiv. 



There are, however, still some questions in dispute 

 regarding this microbe. Is it a tiagellate bacillus, as 

 Migula calls it, or is it a nonrflagellate bacterium, as most 

 authors think, or is it only one stage in the history of an 

 organism which passes through a complex life-history ? 



Professor Koch tells us that outside the human body 

 the plague microbe has a very brief vitality, at most eight 

 or ten days, and that it is impossible to keep it alive longer 

 than that, I believe all authorities are agreed on the 

 truth of this statement. 



We are therefore bound to inquire what becomes of the 

 plague microbe during the long intervals that occur between 

 two epidemics. It must be living somewhere or somehow, 

 for the epidemics reappear at long intervals. In history, 

 plague was first described as an Egyptian disease by liufus, 

 100 A.D. It appeared in Europe in the time of Justinian, 

 5G7 A.D. : again as the Black Death, in 1347 a.d. ; and 

 lastly in 1655 a.d., in the time of Charles 11. Since 1722 

 it has been confined to Asia and Africa. 



In some parts of the Himalayas it reappears almost 

 every avitumn, and disappears at the beginning of next 

 summer; but' even this seasonal prevalence has to be 

 accounted for. 



We use the word microbe vaguely, but before we call an 

 organism a bacterium, it must correspond to the botanical 

 definition of the family of JJaclcriacecv. It must be a small 

 single-celled plant, without chloro{)hyll, reproducing by 

 cross division, or by the formation of spores, and almost 

 always associated with decomposing albuminous substances. 

 Now the plague microbe, outside the body of an animal, 

 does not reproduce itself, either by division or by spore 

 production, but sends off long threads, which drop off and 

 fall down like stalactites, and then the organism perishes. 

 As Dr. Patrick Alanson said at the opening of the London 

 School of Tropical Medicine — " Except in a very limited 

 class, bacterial disease can be acquired anywhere and 

 everywhere ; the only exception to this generalisation is 

 in the case of those bacterial diseases whose germ is a 

 bacterium, which, though usually existing as a saprophyte, 

 may, under certain circumstances, become parasitic." 



Py this, Dr. Manson means a plant having a complex 



