8 QUATERCENTENARY STUDIES IN PATHOLOGY 



It was evident, from the investigations of Professor W. J. Simpson, 

 that much was to be gained by regular and systematic examinations of 

 all rats, dead or alive, and further, his experience of plague in South 

 Africa pointed to an intimate association between the rat epizootic and 

 the human epidemic. 



Accordingly, on my arrival in Hong-Kong, arrangements were made 

 to have as many rats as possible collected from the various Health 

 Districts of the Colony, and forwarded to me for bacteriological 

 examination. Liberal assistance for the methodical carrying out of this 

 research was provided by the Government. Four bacteriologists were 

 obtained from Japan, and assistants were requisitioned from the College 

 of Medicine in Hong-Kong. The following bacteriological methods 

 were employed : — Exact details as to the place where each rat was found 

 was furnished by the Sanitary Department. The post mortem examina- 

 tion on each rat was made under antiseptic precautions, and smears, 

 both of the heart blood and spleen pulp, were made on microscopic 

 glass slides. These were dried, fixed, stained by the usual tinctorial 

 methods, and examined microscopically. In almost all cases, plague 

 infection in rats is most pronounced, the smears usually containing 

 millions of typically oval, bipolar, plague bacilli. Unless the bacilli 

 were typical in appearance and present in enormous numbers, a positive 

 diagnosis was never made. If any doubt existed as to the nature of the 

 organisms present, Gram's method of decolorisation was employed as a 

 counter test. 



From time to time, cultural tests were also made. Owing, however, 

 to the enormous number of rats examined daily by such a limited 

 staff, the microscopic and tinctorial methods of examination were the 

 only possible means of arriving at a diagnosis. Subsequent to the post 

 mortem examinations, all the rats were cremated in an apparatus erected 

 in the immediate neighbourhood. 



T\i^post mortem and bacteriological examination of large numbers of 

 living and dead rats, is a research which must be carried out with 

 considerable care. The diagnosis of the presence of plague bacilli in any 

 tissue or organ, by means of the microscope alone, is frequently one of 

 extreme difficulty. This is all the more so, because, in the tissues of 

 man and animals, micro-organisms occur, which by the microscope alone 

 cannot under any conditions be distinguished from the plague bacillus, 



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