Studies on Tricercomonas Intestinalis (Wenyon and O'Connor, 1917)

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  • Department of Comparative Pathology, Harvard Medical School, Boston, Massachusetts


Tricercomonas intestinalis of Wenyon and O'Connor, 1917, has been found and described for the second time in the United States. The study of the flagellate from this case furnishes the following morphological features in addition to those previously reported.

This intestinal parasite of man is a small flagellate measuring 4 to 10µ in length and 3 to 6 µ in width. It may be ovoid or rounded, but under favorable conditions it shows a caudal protoplasmic protuberance, which makes the organism priform in shape when viewed from the side. One side is flattened and the other convex.

The nucleus, ovoid or rounded, is situated in the anterior end. It has a round or ovoid karyosome and distinct nuclear membrane. Two blepharoplasts are present lying between the nucleus and the flattened side. The anterior blepharoplast gives origin to the 3 anterior flagella. The posterior blepharoplast gives rise to the posterior recurrent flagellum that is adherent to the protoplasm of the body and caudal protoplasmic process, and then emerges as a free fibril. It is stronger than the anterior flagella.

Tricercomonas intestinalis cysts measure 6 to 8µ in length and 3.5 to 5µ in width. They are ovoid in shape and possess 1, 2 or 4 nuclei. Binucleate cysts predominated.

Tricercomonas intestinalis was cultured for three weeks in a medium composed of whole egg slants covered with a mixture of Locke's solution (8 parts) and human serum (1 part); it is called the L. E. S. (Locke-egg-serum) medium.

The flagellate divides by binary fission with the nucleus passing through changes somewhat similar to those found in metazoan mitosis.

This paper, with that of Lynch (5) establishes the validity of the genus and species of Tricercomons intestinalis as separate and distinct from that of Enteromonas hominis.