Page:Tropical Diseases.djvu/755

XL] Morbid anatomy and pathology. The filaria not generally pathogenic.—In most cases of filarial infection the parasite exercises no manifest injurious influence whatever. In a certain proportion of instances, however, there can be no doubt that it does have a very prejudicial effect on its host; and this mainly by obstructing lymphatics. The



healthy, fully formed microfilariæ—that is to say, the larval filariæ which, by means of the microscope, we see in the blood—have, so far as we can tell, no pathogenic properties whatever; the parent worm and the immature products of conception, alone, are dangerous.

Filarial disease originating in injury of lymphatic systems.—Roughly speaking, the filaria causes two types of disease: one characterized by varicosity of