INSECT ENEMIES OF LIVE STOCK 193 



The affection caused by these parasites is a contagious 

 disease, and, once introduced on a farm, will rapidly spread 

 from bird to bird. It has never been shown how and 

 when these mites leave the air sacs, but it has been 

 abundantly proved that they rapidly dry up and die when 

 exposed to the air ; they probably gain access to the avian 

 body by entering the nostrils and following the trachea 

 and bronchial tubes till they reach the air sacs. 



A CANINE DISEASE 



Fil arise do not confine their attacks to human beings, but 

 certain species are also internal parasites of other mammals 

 and birds. One of the most widely distributed of these 

 parasites is Filaria immitis, the " cruel filaria " of the dog, 

 which occurs in various swampy parts of the world and 

 even of Europe. Sporting dogs, probably on account of 

 their more frequent exposure, suffer more frequently than 

 house dogs. 



As in the case of Filaria bancrofti, the causative 

 organism of elephantiasis, the adult parasitic worms occur 

 in the blood vessels ; but, unlike bancrofti, the larvae may 

 be found in the peripheral circulation by day, though they 

 are far more numerous by night. The larvae collect, for 

 the most part, in the right ventricle of the heart, where at 

 times as many as fifty may be coiled together in a bundle. 

 Weakness and shortness of breath are the result, and 

 violent exercise may cause temporary insensibility, whilst 

 the attacks usually end fatally. Anopheles maculipennis 

 and other mosquitoes of the genera Anopheles and Culex 

 transmit the parasites from host to host. Within the 

 kidneys of the mosquito development takes place, and in 

 about twelve days they pass thence from the insect's 

 mouth parts, and the infection is ready to be passed to 

 another canine host. 



13 



