11 



Onee loose it bores through the 

 stomach wall of the mosquito, gets into 

 the muscles, and changes its form very 

 considerably. Finally, after some 16 

 days, h appears in the head and pro- 

 boscis, not in the poison glands as did the 

 sporozoites of malaria, but coiled up 

 under the pharynx and in that part of 

 the proboscis known as the labium. They 

 can remain here for an indefinite period 

 awaiiing the chance to pass into the 

 tissues of a warm-blooded vertebrate 

 when ibe mosquito lakes its next meal of 

 blood. Apparently they can discriminate, 

 for no amount of feeding of the insect on 

 banauas or other fruit (upon which it 

 ordinarily subsists, will cause them to 

 come out. When, however, the insect 

 ■ticks its proboscis into a human being 

 the fiiariae find their way through a weak 

 spot which exists in the labium where 

 the labellae splay out, and pass along 

 the track of the proboscis into the tissues 

 of the victim. The filariae apparently 

 endeavor to emerge in pairs, male and 

 female, and upon establishing themselves 

 in tbe tissues of iheir new host, they set 

 up housekeeping, and begin again the 

 process of which we know the results 

 undfir ibe name of the filariasis, be it 

 €leph**Diiasis or any of the other peculiar 

 conditions by which we recognise the 

 blockios of the lymphatic channels by 

 their offspring. 



I trust that I have been able to give 

 some indication of the very promi- 

 nent part played by certam insects 

 in certain exotic diseases, but there is 

 little doubt that they also assist in 

 disseminating others which are with 

 us already. The ordinary house fly 

 is ubiquitous in its habits and unpleasant 

 in his history and associations. That it 

 is capable of conveying on its feet 

 and body the germs of disease under 

 experimental conditions has been demon- 

 strated and that it frequently does so in 

 nature is freely admitted. In a more en- 

 lightened age the housewife will regard 

 flies wirb the same horror and disgust as 

 she now regards bugs and fleas, 

 and most thinking folk will even now 

 cordially agree with her in theory if not in 



practice. From the time in which it is 

 engendered in a heap of manure to the 

 fateful hour in which it commits suicide 

 in the milk jug, or perishes in the sticky 

 recesses of the summer butter pat, the life 

 of the average fly is passed amidst more 

 than questionable surroundings. Its 

 ubiquity renders the whereabouts of its 

 last alighting place a subject for uncanny 

 speculation when it settles on an article 

 of food, and I have little doubt that 

 domestic flies, so-called, are responsible 

 for a fair proportion of cases of communi- 

 cable disease, especially perhaps of typhoid 

 fever. Its possibilities, however, do not 

 end there ; exanthematous diseases, 

 especially perhaps smallpox, may be 

 readily conceived as spread by this means. 

 I confess in fact to a doubt as to whether 

 the real cause of the aerial convection of 

 smallpox is not partly or wholly due to 

 insect life. Many points in the available 

 evidence upon it appear to render such a 

 hypothesis tenable, and £y proof door and 

 windows coverings should certainly form 

 a part of the furnishing of isolation hos- 

 pitals for this disease. 



The possibilities of this line of research 

 are, however, boundless, and in time to 

 come the labors of tbe biologist and 

 naturalist will become of luore and more 

 importance from the standpoint of human 

 disease. The extension of research in 

 connection with cancer in the lower 

 animals has resulted in its discovery in a 

 large number of creatures, including even 

 fish. Similar results have been obtained 

 with the tubercle bacillus, whose range 

 appears to be practically universal. The 

 diseases of which I have spoken tonight 

 do not by any means include all those 

 in respect of which insects are known, or 

 suspected, to play an important or essen- 

 tial part, but they will serve as illustra- 

 tions of the pioneering work which has 

 been, and is daily being done by many in- 

 vestigators in different parts of the world 

 for the benefit of humanity and the 

 advancement of civilisation. 



The lecture was illustrated by lantern 

 slides. 



