This section is from the book "Diseases Of The Intestines", by Max Einhorn. Also available from Amazon: Diseases Of The Intestines A Text-Book For Practitioners And Students Of Medicine.
Most of the animal parasites found in man inhabit the intestinal canal. Leuckart 1 estimates the number of varieties at about fifty. Not all parasites, however, produce morbid conditions. Comparatively few of them evoke a pathological state, either in the intestine by their direct presence, or in the blood by the formation of toxic products which are absorbed and reach the circulation. The intestinal parasites are detected by repeatedly examining the stools. They may be seen or their presence may be assumed from the discovery of their ova (the latter referring to the helminths). There are no characteristic symptoms which would be encountered only in morbid conditions due to animal parasites. The diagnosis, therefore, must be made by directly discovering them or their eggs in the dejecta. It will always be wise to look for worms in cases in which gastric and intestinal symptoms of a functional character exist, accompanied or not by anaemia and certain neuropathic affections. The intestinal parasites are divided into two large groups: (1) Protozoa. (2) Vermes.