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476 
with serum. The efficiency of the extirpation and of the serum treatment 
depend on the stage of plague development which exists at the time they 
are instituted ; when performed in an early stage, a favorable result may 
be expected, but in a later one these measures become futile. As a con- 
sequence, it is important to obtain a positive diagnosis as early as possible, 
That good results may be obtained from serum treatment in such cases 
admits of no dispute. During the first outbreak in Osaka, Yersin’s serum 
was used, but owing to the scarcity of the supply of this.remedy, the 
results fell short of our expectations. Since 1900 our institute has been 
preparing the serum to meet with the constant demand. For the patients 
actually suffering from the disease, comparatively large quantities (200— 
240 cubic centimeters) are required for inoculation, and although we 
are not in a position to ascribe to the pest serum a value as absolute as 
to the diphtheria serum, there is no doubt of the efficacy of the former 
remedy. ‘The following facts demonstrate this: 
A series of experiments was conducted in the Tainan isolation hospi- 
tal (Formosa) with the view of comparing the results of the serum with 
those of an early extirpation of the buboes and general systematic treat- 
ment. Of the 56 patients treated by the latter method, 35 (62.5 per 
cent) died of plague, while out of the same number inoculated with 
serum the death rate was only 33.9 per cent. From these experiments 
it is seen that the use of the serum reduced the death rate by about one- 
half. Our experience during the epidemics in Japan has shown that the 
most effective treatment is that in which both serum inoculation and 
extirpation of the buboes are performed in as early a stage of the disease 
as possible. 
RATS AS THE PROPAGATORS OF PLAGUE. 
The fact that rodents are always closely connected with an outbreak 
of plague (in all times and places) admits of no dispute. ‘The epidemics 
in Japan have invariably been traced to rats. 
Obviously these animals have a high susceptibility to the pest infection ; 
their habits also constantly bring them in contact with filth in which the 
plague germ is present, besides which they feed upon one another. These 
facts must favor the spread of plague. The finding of human victims 
of the pestilence is almost invariably preceded by the discovery of plague- 
infected rats. Hence the killing of rats must be resorted to as the first 
and most important step in the prevention of an epidemic. In the first 
outbreak in Osaka and Kobe the pestilence was gradually stopped by an 
urgent effort directed at destroying these rodents; and the ones in Tokyo 
and Yokohama were confined to a small area by the strict enforcement 
of these same measures. The number of rats killed in Tokyo since 1900 
and up to the present time amounts to the enormous figure of 4,820,000— 
that is to say, the average is more than 800,000 a year. In other words, if 
these dead rats were laid side by side they would extend for a distance of 
