November 3, 1910] 



NATURE 



I 



lief demand of the present time is for 'spade 



orkers ' and * quarrj-men ' to prepare foundations 



-:d material." It is to be h<^)ed that on this point 



: least the Board ^ill allow itself -to be converted. 



nless men of outstanding ability can be attracted to 



.:• research stations and agricultural «rfleges, there is 



c much hope that the taxpayer will see anything 



<e the return he ought for the money expended. 



his., indeed, is the \-ital question ; if the right sort 



: men are got to do the work all tfie other questions 



: administration sink into insignificance. But here 



so the Board is m what appears to be the safF> 



ound. The idea of a central experimental station 



dismissed, and a wider policy is suggested : — '" It 



uld probably be advisable, therefore, to use part of 



e Develc^ment Fund in making such grants to 



iversities and imiversity cc^eges as would induce 



em to make provision fw agricultural research." 



At no period in its history has agricultural science 



vl a greater opp«-tunity than at present. It is no 



"ger hampered by lack of funds or by apathy on 



■? part of the farmer. The problems are more 



imerous and more interesting than ever they were. 



ut unfortxmately the workers are few. and fresh 



rkers are not readily forthcoming. The hopeful 



ature is that a number of eminent men of science are 



ving up time and thought to the organisation of the 



■X work, and, further, that the Board of Agriculture 



:.d the large agricultural societies are manifestly and 



. nuinely anxious to render all die help they can. 



RATS AND PLAGUE. 



ALTHOUGH the recent epidemics of bubonic 

 plague in China, India, and other parts of the 

 world have been always associated with outl»-eaks of 

 die same disease amongst rats, the historical study of 

 plague throughout the world reveals the singular fact 

 that previous to 1800 very few references to a coin- 

 cident mortality amongst rats have been put on record. 

 Many excellent accounts of the older outbreaks, 

 notably of the Black .Death in Eurc^ in 1347, and 

 the Great Plague of London in 1665, are in existence, 

 but careful research into these documents by nkidem 

 historiographers — Haeser, Hirscfa, Abel, and Sticker — 

 has shown that for reascms difficult to discover very 

 scanty mention of associated rat mortality has been 

 made. 



The earliest recorded instance is perhaps that given 

 in the Bible in the account of the pestilence amongst 

 die Philistines, which they ascribed apparendy to 

 "the mice diat marred the land." Avicenna refers 

 to the assooadmi between rats and plague in his 

 description of the epidonic in Mesopotamia about the 

 year 1000 a.d. Nicephorus Gregoras, writing of the 

 Great Plague of 1348, which entered Europe by way 

 of Constantinople, makes a similar reference. Rats 

 are mentioned in connection with the plague in Yun- 

 nan about 1757, and later in 1871-3. In India an 

 association between rats and plague is noted in the 

 Bhagaeata Purana. by the Emperor Jefaangir in the 

 plague epidemic of 1615, and in a report of the Pali 

 plague in Rajputana in 1836. Lastly, Orraeus refers 

 definitely to rat mortality in his account of the 

 epidemic of 1771 in Moscow. 



• The identity of the disease in rats widi that affecting 

 man was established hv die discovery in 1894 of B. 

 Pestis by Yersan and Kitasato. 



Within the next few years the relationsfaip between 

 rat and himian plague was investigated in manv parts 

 of the world— by Thompson and Tidswell in Svdnev, 

 Clark and Hunter in Hongkong. Snow, Weir, Hankin 

 and James in India, and bv Kitasato in Japan. In 

 tqo=i die Plague Research Commisaon was appmn^ed 

 to investigate plague in India, and the reports of this 

 NO. 2140, VOL. 85] 



Commission represent the results of the most exhaus- 

 tive inquiry into the subject that has yet been carried 

 out. 



The JCommission early turned its attention 10 the 

 relationship of rat plague and human plague, and 

 instituted an extensive examination of the rats in 

 Bombay and elsewhere for the presence of plague in- 

 fection. The maps and charts, representing graphic- 

 ally the results of this examination, clearly show ihe 

 correlation between the epizootic and the epidemic — 

 the rat epizootic preceding the epidemic by an interval 

 of ten to fourteen days. Every outbreak of bubonic* 

 plague, -«'hen .adequately investigated, was found to 

 be associated with the disease amongst rats. The 

 conclusion must be drawn that e\'ery epidemic of 

 bubonic plague is caused by the ccmcomitant rat 

 plague. 



In Bombay the rat population is an enormous one, 

 Mus decumanus (the brown or grey rat) swarming in 

 the sewers, gullies, and outhouses in the cit\', and 

 Mus rattus (the black rat) living in countless numbers 

 in the houses of the people. The latter species is of 

 especial importance in plague epidemics, because it is 

 essentially a house rat: it may almost be said to be 

 a domesticated animal. The severity of the epizootics 

 in the two q>ecies will be appreciated when it is stated 

 that during mie year die examination of 70,789 M. 

 decumanus, taken frmn all parts of BcMnbay city, 

 proved that 13,277 were plague-infected = 18^8 per 

 cent., and that out of 46,302 If. rattus examined 4,381 

 were plague-infected =9*4 per cent. The heavier 

 incidence of plague in If. decumanus is explicable ty 

 the circumstance that the flea infestation of diis species 

 is more than twice that of M. rattus. 



Some interesting observations on the distribution of 

 different ^)ecies of rats in India have been made 

 recendy by Captain R. E. Lloyd, I. M.S. The most 

 commcm rats in India are M. rattus, M. decumanus, 

 and Gunomys {Nesokia hengalensis). M. decumanus 

 is common both in Bombay and Cakrutta, but is 

 absent from the city of Madras. It is significant diat 

 Madras is the one port in India which has never been 

 seriously infected with plague. \l. rattus appears to 

 be universally distributeid in India, whereas JJf. decu- 

 manus does not seem to occur in India except in sea- 

 ports. Nesokia hengalensis is found in even' part of 

 India. 



The qutetion of the transportation of plague by 

 ship rats is an extremely important one, but has not 

 so far been thoroughly wcMlced out. It would appear 

 that M. decumanus is the spedes most commonly in- 

 festing ships, although Af. rattus is also found. 



Sticker, in his history of plague epidemics, quotes 

 the statonent that M. decumanus got into Europe 

 from Persid about the year 1725. In England Af. 

 rattus was displaced bv the inva^on of If. decumanus 

 about this time. At the present day the predominat- 

 ing species in this country' is undoubtedhr M. decu- 

 manus i M. rattus is, however, becoming increasingly, 

 commcm in the seaports. 



.^n important question in plague epidemiolf^ is the 

 mode of convCT-ance of the infective organism from the 

 plague rat to man. It is impossible even to sum- 

 marise here the numerous experiments and observa- 

 tions on this subject, but it may be said that from 

 many sides, and espenally from e x per im ents in the 

 laboratory and in actiial plague^infected houses, a mass 

 of evidence has been raised whidi incriminates and 

 indeed convicts die rat flea as the transmitting agent 

 of the infection. 



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