58 



on the outskirts beyond the ramparts 2 per cent, were infected, 

 whilst within the native town proper, entirely surrounded by hig'h 

 fortifications, the proportions were from 25 per cent, to 30 per 

 cent., and this notwithstanding that the number of dogs in pro- 

 portion to the number of inhabitants is practically the same all 

 over the town. 



The insanitary conditions due to ponds, stagnant water, and 

 organic filth around the houses are the same everywhere, only the 

 houses in the citadel and its immediate neighbourhood are closer 

 together, better sheltered from wind, and to a certain extent from 

 variations of temperature. The population is also denser. The 

 dogs in all cases roam about the houses at will, and rarely or 

 never go out into the surrounding country, and this leads to the 

 conclusion that canine filariasis is transmitted by some agent 

 which exists in human dwellings, and that it there finds the 

 most favourable conditions for its development. 



Ticks {Ixodes ricinus) and Hippohosca (H. capensis) by reason 

 of their abundance first attracted the authors' attention, some 

 dogs being found literally covered with them. Tabanids, 

 Sto77io,vys, etc., only rarely bite bogs, and the authors on examina- 

 tion failed to find any organisms in them. 



They carried out experiments in the following manner : — A 

 large cage 3x1x1 metres, entirely closed, with glass windows 

 and wire gauze walls, was divided into two compartments by coarse 

 wire-netting through which flies could pass easily. In one com- 

 partment were placed vessels containing the larvae of mosquitos 

 collected about the Annamite houses in those quarters where dog 

 filariasis was common. The cage was placed under a veranda, so 

 that the conditions under which the insects were placed were as 

 nearly as possible similar to that of their usual enA'ironment. 

 Forty-eight hours after the insects developed from the larvae, a 

 dog suffering from filariasis was introduced into the large cage 

 with the insects. The female Stef/omyia attacked it vigorously, 

 gorging themselves with blood and then resting on the walls of 

 the cage where it was easy to take them. All the insects which 

 had bitten the dog on one and the same occasion were collected 

 in a cage and fed with Avater and bananas, and the development 

 of the Fila/ia was followed in their bodies by the dissection of one 

 of their number at frequent intervals. It was discovered that 

 the embryo required nine days, at 31-35° C*., to pass from the 

 microfilaria stage in the stomach to that of the larva in the pro- 

 boscis ; these early metamorphoses take place in the Malpighian 

 tubes, as other writers have demonstrated to be the case with 

 Dirofilnria ivnnith. They then traverse the thoracic muscles and 

 lodge themselves in the proboscis where they behave in the same 

 way as has been observed of F . hancrofti in Cvlex and Anopheles 

 by various writers. The authors never found more than four or 

 five Filai-ia in the thoracic muscles of the same insect even when 

 the original infection was gross. The development of the 

 embryo in the intermediate host is greatly affected by the tempera- 

 ture. In Jrme, July and August metamorphosis was complete 

 in nine days in a laboratory temperature of 25° C. to 30° C. 

 When the temperature in September ranged from 21° C. to 23° C. 



