(\ exvr ~) 
the Journal of Hygiene, but I wish to bring to your notice 
how the development of Bacillus pestis in the alimentary 
system of the flea causes it to convey infection through its 
mouth. The alimentary system of the flea includes a long 
sharp tubular pricker formed by the opposition of the mandibles 
and epipharynx, through this tube the blood is drawn, owing 
to the action of a powerful pump in the head of the flea. From 
the pump the blood passes along the oesophagus, a narrow 
but elastic tube, to the proventriculus or gizzard on its way 
to the stomach. The proventriculus when at rest is shaped 
very much like a tangerine orange ; internally it is armed with 
a series of rings of slender curved chitinous spines; externally 
it has a series of hoops or belts of muscles. Normally this 
organ forms an efficient valve, owing to the constriction of the 
muscular bands narrowing and elongating the organ, and 
causing the spines to meet in the centre. 
After a meal of infected blood, the ingested bacilli become 
the starting-points of colonies which increase in size until they 
cause the stomach contents to be of a lumpy nature, and 
finally the stomach may be completely filled with a solid mass 
of plague culture, which can be removed on dissection like 
jelly from a mould. At the same time the bacteria also 
multiply among the spines of the proventriculus, clogging its 
action and blocking the passage to the stomach. The pumping 
apparatus is, however, still efficient, and further feeding not 
only tends to distend the proventriculus, but the oesophagus 
as well, the blood in the latter being under pressure in an 
elastic tube. The bacteria develop in this fresh blood where it 
comes into contact with the obstructing mass of plague culture, 
and the possibility of the flea regurgitating a blood culture of 
Bacillus pestis into the next wound it makes is brought about. 
In some instances continued efforts on the part of the flea 
enable it to get some blood past the stoppage, but in many 
instances the mass of bacteria develops forward into the 
oesophagus, forming a solid cone in front of the entrance to 
the proventriculus; in this case the flea’s efforts are in vain. 
Meanwhile the jelly-like mass in the stomach gradually dis- 
integrates and passes out of the flea, as the supply of nutriment 
for the bacteria becomes exhausted. 
