81 



LECTURE II. 



THE TRANSMISSION OF PLAGUE BY FLEAS. 



MR. PRESIDENT AND GENTLEMEN, May I remind you 

 that bubonic plague is not an infectious disease ? The 

 patient is a negligible source of danger to his surroundings, 

 provided he does not develop a secondary pneumonia. The 

 reason is that even if the excreta do contain some plague 

 bacilli, there is no mechanism available to convey them into 

 a second human being, as pest is not easily contracted by 

 feeding. From an epidemiological point of view bubonic 

 plague must be regarded as a disease of rats, in which under 

 suitable conditions the infection spreads from rat to man. 



It would be impossible for me to put before you this after- 

 noon the mass of evidence for the above statements. I have 

 already surveyed it in opening the discussion on the spread 

 of plague at the meeting of the British Medical Association 

 at Birmingham in 1911 (Martin, 1911), and, moreover, it is 

 now well known. 



It was difficult to explain how the bacillus was trans- 

 ferred to man from the rat, especially as man to man 

 infection had been shown to be negligible. On epidemio- 

 logical grounds Ogata (1897), Simond (1898), and Ashburton 

 Thompson (1900) came to the conclusion that the agent must 

 be some form of insect, and for various reasons choice fell 

 upon the flea. You will naturally inquire why, if the flea 

 is to be considered an agent of transmission from rat to 

 man, does it not transmit from man to man ? The answer is 

 quite satisfactory, but I will, with your permission, postpone 

 it until we have considered the case for carriage from rat to 

 man. 



If the blood of the animal contain a sufficiency of plague 

 bacilli, some will obviously be taken in by a flea whilst 

 feeding, and Ogata (1897) found that crushed fleas taken 

 from a plague-infected rat produced the disease when 

 injected into mice. This experiment was repeated with 

 success by Simond (1898) and Tidswell (1900). 



