1* 



10 



meal of infected blood, and examining 

 them under a microscope, large numbers 

 of bacilli indistinguishable from plague 

 bacilli in their microscopical characteris- 

 tics, were found in a peculiar organ form- 

 ing a part of the oesophagus ; while in fleas, 

 which had been fed on healthy blood, no 

 such bacilli were found. 



The work which I have alluded to was 

 performed in India certainly with all the 

 facilities of one of the biggest bacterio- 

 logical laboraties in the world, but without 

 much assistance from special literature on 

 the subject, for the very good reason that 

 none existed to indicate the technical 

 difficulties to be overcome. As you may 

 readily imagine, these were considerable, 

 for to secure such an active and minute 

 creature as the flea in such a manner as 

 to allow it to feed, and yet to ensure that 

 it should not get away after its dangerous 

 meal of plague infected blood, was an 

 operation of no little difficulty, and also 

 of some danger, both to the experimenter 

 and to his neighbors. After a good deal 

 of trial, the device was hit upon of 

 confining them in a glass tube — an 

 ordinary test tube was used — and covering 

 the open end with a cap of fine gauze, 

 through the meshes of which the flea 

 could protrude its proboscis, but could not 

 escape. This difficulty overcome, it was 

 necessary to find some distinguishing 

 marks by which to identify the species 

 used. This was affected after a 

 time, and the few species employed were 

 readily enough identified. 



The habitual spread of plague by fleas 

 of the type I have shown you is not to be 

 taken as a universally accepted fact, but 

 strong evidence exists that this will 

 eventually prove to be, at any rate, an 

 important factor in epidemics. 



You may recollect an allusion made to the 

 work of Dr., now Sir, Patrick Manson, m 

 relation to certain blood worms, which 

 are fairly common amongst human beings 

 in the tropics. No less than five difi'erent 

 kinds of these worms are known, and 

 one in particular, the filaria nocturna, so 

 called because it is only found in the 

 blood during sleeping hours, is of par- 

 ticular interest, in that it causes a good 

 deal of illness by blocking up the deli- 

 cate lymphatic ducts, and is almost cer- 

 tainly in this way the cause of that 

 strange disease elephantiasis. Filariae 

 occur amongst other tropical and 



subtropical places in Queensland and 



Northern Australia to about the lati- 

 tude of Brisbane, and the manner in 

 which the filaria noctutna completes 

 its Hfe cycle is of interest. The 

 parent female worm is some 4in 

 long, and lives in some part of the 

 lymphatic system, in company with the 

 male, which is slenderer and smaller. 

 There she produces a great number of 

 embryos, which make iheir way into the 

 blood, and live during, the day in the 

 vessels of the internal organs. About 5. 

 or 6 p.m., in infected persons who do their 

 sleeping at night, they begin to appear in 

 gradually increasing numbers in the peri- 

 pheral circulation, or vessels in the ex- 

 tremities and at the surface, increasing 

 till about midnight, and then decreasing, 

 until about 8 or 9 in the morning they 

 have all disappeared from the peripheral 

 blood for the day. It is a curious fact 

 that in infected persons, who do their 

 sleeping during the day and remain 

 awake at night, the embryos reverse the 

 time of their appearance, and turn up 

 during the day in the peripheral vessels, 

 disappearing at night. Each embryo is 

 about l*80in long, and is contained in a 

 loose sheath or sack somewhat longer 

 than itself. They are very active organ- 

 isms, and wriggle about strongly, but the 

 sheath keeps them from changing their 

 position much ; in other words, they are 

 not locomotory. The function of 

 the sheath is to keep them from 

 using the strong boring apparatus which 

 they have on their heads, and so escap- 

 ing from the blood vessels. As I have 

 said, they appear in the surface blood 

 vessels at night as a rule, and this is 

 obviously for the convenience of the con- 

 veying mosquito, which principally feeds 

 at night, and into whose stomach some 

 of the embryos are taken with the meal 

 of blood. The ordinary mosquito so act- 

 ing is a species of Culex, and in its stomach 

 the blood becomes much thicker by co- 

 agulation. The embryo within the sheath 

 is thus able to get a purchase on the 

 sheath, and eventually to ram its way 

 out through one end by butting vigor- 

 ously while the sheath is stuck fast in 

 the thickened blood. Of course, while 

 the blcod was fluid in the human host's 

 vessels, it could not do this because the 

 sheath could only be bumped along by 

 its effortB from within and would not split. 



