August 30, 1912] 



SCIENCE 



267 



should now call it. Paludism, the influence of 

 marshes, could not be seen; what could be 

 seen were fogs or vapors rising from the 

 marshy ground and these were blamed for 

 spreading malaria, and people were told to be- 

 ware of the damp and of night air. But why 

 vapor, whether in the daytime or at night, 

 should breed any kind of disease, most of all 

 so definite a disease as ague, was not at all 

 obvious. At last all these vaguenesses were 

 dispelled, and malaria was discovered (1880) 

 to belong to that already large group of dis- 

 eases known as parasitic, only the parasite in 

 this ease was an animal and not a vegetable. 

 Ague was found to be due to the destruction 

 of the red blood-corpuscles by their having 

 been made the residence of a minute animal 

 parasite, the Plasmodium malariw, which had 

 been inoculated into the patient through his 

 having been bitten by a particular kind of 

 gnat or mosquito {Anopheles) which had 

 sucked blood from some one suffering from 

 malaria. It was not contagion, nor ordinary 

 infection, far less bad air or vapors or exhala- 

 tions, it was natural, accidental inoculation 

 with foreign blood containing excessively mi- 

 nute living creatures classed by zoologists as 

 a species of Protozoa. 



Thus the connection of malaria with 

 marshes and vapors and night-time was at 

 once explained by the facts that the mos- 

 quito lays its eggs in damp places and fre- 

 quents damp places towards evening and 

 after dark. The meaning of the usefulness of 

 quinine is explained by its being able to kill 

 the parasite in the blood; it is only a local, 

 circulating germicide. Thus the microscopist 

 has tracked down one of mankind's subtlest 

 foes, found it neither mist nor marsh, vapor 

 nor corruption, but a moving, living creature, 

 a member of the lowest group of such known. 

 The vagueness has gone; the cause of ma- 

 laria can be viewed sealed up in Canada bal- 

 sam under a cover-glass. 



Another excellent example of the rendering 

 definite what was before of the vaguest is the 

 recent discovery of the cause of plague, the 

 pestilence, or Black Death. In the fourteenth 

 century the great surgeon of Avignon, Guy de 



Chauliac, attributed the plague to a conjunc- 

 tion of the planets Saturn, Jupiter and Mars 

 in the sign of Aquarius on the twenty-fourth 

 of March, 1345. About the same time the 

 Jews in Germany and Switzerland were sus- 

 pected of poisoning the wells, and were in 

 consequence persecuted and massacred. In 

 the fourteenth century the medical faculty of 

 the University of Paris was asked to deliver 

 an opinion on the nature and origin of plague, 

 but a very great deal that it promulgated was 

 absolutely fatuous as regards protection or 

 cure. One thing only was recommended that 

 is interesting in the light of to-day, namely, 

 the fumigation of houses by the burning of 

 aromatic herbs and woods. Only as recently 

 as 1894 was the vera causa of the Black Death, 

 one of mankind's most terrible traditions, dis- 

 covered by two Japanese doctors, Tersin and 

 Kitasato, and named the Bacillus pestis. It 

 was soon isolated in pure cultures and grown 

 in artificial media, and its toxins and anti- 

 toxins became chemical entities. 



The history of the discovery of what plague 

 is really due to is a strange, eventful history. 

 The Black Death, that most dreadful scourge 

 of mysterious origin, was for centuries at- 

 tributed to such sources as the conjunction of 

 planets, the iniquities of the Jews or to some 

 special outpouring of divine wrath on account 

 of human sin. Mankind, utterly at a loss to 

 discover its true relationships, had for mil- 

 lennia imagined vain things, and essayed the 

 most grotesque methods of averting it. But in 

 the fullness of time the microscope was de- 

 vised and with it the dawn of the day of exact 

 knowledge had arrived. 



The source of plague was shown to be a ba- 

 cillus, a most minute, vegetable parasite which, 

 growing in bodies of certain animals, rats and 

 other rodents, could give rise to a most viru- 

 lent poison (pestiferin) which was carried to 

 all parts by the circulating blood. It was 

 further shown that man became inoculated 

 by fleas which had been feeding on the ba- 

 cilli-containing blood of rats; and thus were 

 revealed the several links in that long chain 

 which had the Bacillus pestis at one end and 

 man at the other. It took mankind 3,000 



