84 



from the diagrams (Figs. 13, 14, and 15), which are borrowed 

 from the reports of the Commission. 



The average capacity of a rat flea's stomach was found by 

 the Commission for the Investigation of Plague in India 

 (Keport 1907, p. 397) to be 0-5 c.mm., and the number of 

 bacilli in the blood of a plague-infected rat before death 

 anything up to 100,000,000 bacilli per cubic centimetre. 

 If, therefore, a rat flea imbibed the blood of such a rat it 

 would receive into its stomach 5000 germs. 



Evidence of Multiplication of Bacilli in the Stomach of 

 the Flea. 



The Commission fed fleas on plague- infected rats until the 

 death of the latter, and afterwards on healthy animals, a 

 fresh animal being supplied each day. Each day a number 

 of the fleas were dissected, and the stomach contents were 

 examined as to the presence or absence of plague bacilli. In 

 5 to 30 per cent., according to the time of year, plague 

 germs were found up to the sixth day, and in one instance 

 on the twentieth day (Kepprts 1907, pp. 398-405). The 

 bacilli were often present in immense numbers, far more 

 numerous than ever seen in blood, and massed together as 

 in a culture. We have good evidence in this observation 

 that multiplication of plague bacilli may take place in the 

 flea's stomach. 



During the season of the year when the epidemic occurs 

 the proportion of infected fleas for the first four days aftsr 

 .removal from the plague rat was 43 per cent. , on the sixth 

 day there were 15 per cent. , on the eighth day 16 per cent. , 

 and on the twelfth day 9 per cent. In the non-epidemic 

 season only 5 - 2 per cent, were infected during the first 

 six days. 



The Distribution of Plague Bacilli in the Body of the Flea. 



The blood on completion of the digestive process in the 

 stomach passes into the rectum of the flea as a thick, slimy, 

 dark-red mass, and appears at the anus as minute, dark red 

 or black, tarry droplets. It was demonstrated by cultural 

 and microscopical examination that the rectal contents were 

 often crowded with plague bacilli. 



Fleas, taken from plague rats at intervals varying from a 

 few hours to several days, were dissected and the various 

 parts of the body examined for the presence of bacilli. In 

 not a single instance were any plague bacilli observed 

 outside the organs already mentioned. No infection of the 

 body cavity was seen, and, although particular attention was 

 paid to the salivary glands, nothing at all resembling a 

 plague bacillus was ever detected in them. 



