v PLAGUE IN THE EAT 89 



bacteriological evidence in six instances, and in two instances 

 microscopical evidence only. I do not think, however, that mere 

 absence of positive evidence of this sort can properly be regarded 

 as excluding presence of plague among rats ; but such absence 

 must be held to have weight when other circumstances tend to 

 cast doubt upon the assertion that a particular rat sickness was 

 plague. 



Subject to such allowance as may be made for these considera- 

 tions, I proceed to examine in detail the figures I have given under 

 this head. 



As regards the 58 vessels on which plague is not known to have 

 made its appearance save in man, these instances seem to point the 

 moral, at present overlooked by many, that, whatever the degree of 

 danger to persons on board ship from infected rats, the latter condi- 

 tion is not the greatest danger. So marked is the difference between 

 the number of vessels (58) in which human plague only is recorded 

 and the number (28) in which plague is stated to have occurred in 

 both man and rat, that this proposition must, I think, stand, even if 

 some transference had to be made from the first class to the second. 

 These figures certainly do not support the contention that the rat is 

 the chief agency by which plague is transmitted to man. That such 

 view is erroneous is further indicated by consideration of the circum- 

 stances in which plague made its appearance on the 28 vessels in 

 which both man and rat are stated to have been affected. As 

 regards these vessels it has been too readily assumed that it was in 

 all cases the rat that gave the disease to man ; to the exclusion of 

 the consideration that in reality man may have infected the rat. 

 Again, the mere fact that one or two dead rats had been found on 

 board a ship with human plague has been taken, without further 

 evidence, as proof of there having been rat plague on board — with 

 inference that here was the source of the human plague. ..." 



(3) The danger of transmission of infection from ship to shore 

 by plague-infected rats. 



" Under this head I propose to consider, in the first instance, how 

 far plague is known to have spread to places on shore in 1898-1901 

 from the 28 ships stated to have had both human plague and rat 

 plague on board, and from the 9 ships stated to have had rat plague 

 only. 



From 4 of the 28 vessels above referred to, plague is stated 



