Pools containing a border growth of grass or rushes are often selected by anophelines for depositing eggs. The small fish or tadpoles, which prey on the larvae, cannot work their way through the obstacles and, again, petroleum oil cannot be easily distributed in a network of grass. Anophelines of different species and of different countries seem to vary in their selection of water for depositing their eggs. We should not generalize but go out and search for breeding places.
Fig. 15.—Anopheles maculipennis (quadrimaculatus), male. (After Castellani and Chalmers.) From P. H. Reports.
Anophelines seem to prefer small collections of water or sluggish clear streams. The pools made by excavations following railway or other similar construction are favorite breeding places. Proper cultivation of rural districts makes the country more healthful and Carter has stated that tile drainage is the key to rural malaria control.
The most practical method for the identification of anopheline species is to collect the larvae and later to study the adults which develop from the pupae. On the whole culicines do not seem to object to foul collections of water while anophelines avoid such breeding places.
Pathology and Morbid Anatomy
The pathological lesions are those connected with the destruction of enormous numbers of red cells, not only each infected red cell being destroyed but others not so parasitised. There has been an idea that at the time of sporulation and rupture of the merocyte a pyrogenetic toxin was given off and along and with this there were haemolysins and endotheliolysins. Following Brown we are justified in thinking that the malarial pigment (melanin or haemozoin) can act as a haemolysin and by being taken up by endothelial cells bring about their degeneration with associated capillary haemorrhages. All three factors—red-cell destruction by parasites, haemolytic action on red cells and capillary haemorrhages lead to anaemia.
Fig. 16.—Digestive tract of Anopheles the stomach of which is covered with numerous zygotes or oocysts of Plasmodium falciparum. c, cloaca; mt, malpighian tubules; o, oocyst; s, stomach; sb, sucking bladders or pumping organ; sg, salivary gland. (MacNeal from Doflein, modified after Ross and Grassi.)