i68 



Insects and Disease 



but in severe cases the distorted parts often render 

 the patient entirely helpless. 



The exact way in which the parasites cause such 

 swelling is not very definitely known. Manson, 

 who has done more work on these diseases than 

 any one else, believes that the trouble arises from 

 the clogging of the lymphatic glands or trunks, 

 thus cutting them off from the general circulation, 

 in which case the affected parts may become dis- 

 torted. This clogging of the passages is believed 

 to be due to the presence of great numbers of im- 

 mature eggs which have been liberated by para- 

 sites injured in some way before their eggs were 

 entirely developed. 



This interference with the lymphatic circulation 

 brings about the anomalous condition of a patient 

 with a serious filarial disease with fewer of the 

 filarial parasites in his blood than one who is not 

 so seriously affected. This is supposed to be due 

 to the fact that the disease-producing parasites 

 have died and that the lymphatics have become so 

 obstructed that any microfilariae they may contain 

 cannot make their way into the general circulation. 

 Such a patient then would not be as likely to infect 

 a mosquito as would one less seriously affected. 



It has always been thought that little or nothing 

 could be done in the way of successfully treating 



