It is usual to classify the Flagellata in four orders: Euflagellata, Dinoflagellata, Choanoflagellata, and Cystoflagellata, of which only the Euflagellata are of interest to us. This is a group comprising numerous species, for the further classification of which the number and position of the flagella are utilised.
The Euflagellata observed in man belong to the Protomonadina as well as to the Polymastigina. The former possess either only one or two similar flagella, or one principal and one or two accessory flagella. The Polymastigina possess at least three flagella of equal size, or four to eight of unequal size, inserted at different points. An undulating membrane may be present in members of both groups.
It must also be pointed out that unicellular organisms with one or several flagella are not always classified with flagellates, for such forms occur in Rhizopods as well as temporarily in the lower plants. In addition, the examination of the flagellates, especially the parasitic species, is very difficult on account of their diminutive size and great activity; thus it happens that certain forms cannot with certainty be included in the group because their description is insufficient.
Order. Polymastigina, Blochmann.
The Polymastigina contains flagellates with three to eight flagella. Some of the Flagellata parasitic in man belong to the Polymastigina, and to two or three genera that are easily distinguishable.
Genus. Trichomonas, Donné, 1837.
The body is generally pyriform, the anterior part usually rounded, the posterior part pointed. There are at the anterior extremity three (? four) equally long flagella that are sometimes matted together. A blepharoplast (kinetic nucleus) and basal granule are present, together with a supporting structure known as an axial filament or axostyle. In addition there is an undulating membrane, bordered by a trailing flagellum, that commences at the anterior extremity and proceeds obliquely backwards. The nucleus, which is vesicular, is situated near the anterior extremity, and behind it are one or more vacuoles, none of which seems to be contractile. These flagellates are parasitic in vertebrate animals, and live chiefly in the intestine.
Trichomonas vaginalis, Donné.
The form of the body is very variable, and is elongate, fusiform or pear-shaped, also amœboid. The length varies between 15 µ and 25 µ, and the breadth between 7 µ and 12 µ. The posterior extremity is drawn out to a point and is about half the length of the remainder of the body. The cuticle is very thin and the body substance finely granular. At the anterior extremity there are three—some say four36—flagella of equal length which are frequently united together, at least at the base, and are easily detached.
There is an undulating membrane (fig. 16) which runs spirally across the body, arising from the place of insertion of the flagella, and terminating at the base of the caudal process. A cytostome seldom is recognizable in fresh specimens, but is apparently present. The nucleus is vesicular, elliptical and situated near the anterior extremity.37
Multiplication takes place by division (Marchand). Encysted forms are almost unknown.
Trichomonas vaginalis lives in the vaginal mucus of women of various ages, not in normal mucus, but in mucus of acid reaction. It is found in menstruating females as well as in females who have passed the menopause. It occurs in pregnant and non-pregnant women, even in very young girls, provided always that they have a vaginal catarrh with acid reaction of the secretion. Should the acid reaction change, as, for instance, during menstruation, the parasites disappear, as they do likewise on injection of any alkaline fluid into the vagina. A low temperature (below +15° C.) is also fatal to the parasites. These flagellates can pass from the vagina through the urethra into the bladder, and produce severe catarrh, and are not easily removed.
Fig. 16.—Trichomonas vaginalis, Donné. × 2,000 approx. (After Künstler.) Four flagella are represented, but usually only three are present.
T. vaginalis appeared to be a parasite specific to the female organs and not transmissible to man. However, several observations have since been made that confirm the occurrence of this species in the urethra of the male. The infection apparently takes place through coitus when changes are present in the urethral mucous membrane. At any rate, three cases observed point to this circumstance.
Attempts at experimental transmission to rabbits, guinea-pigs and dogs failed (Blochmann, Dock). So far, the manner in which women become infected is unknown.
Trichomonas intestinalis, R. Leuckart, 1879 = Trichomonas hominis, Davaine, 1854.
Some authors believe that a second trichomonad inhabiting man, Trichomonas intestinalis, R. Lkt., is identical with Trichomonas vaginalis, Donné. Leuckart’s species was based on the discoveries of Marchand (1875) and Zunker (1878), who stated that according to all appearances, and in their opinion, it was the same as Cercomonas intestinalis, Lambl, 1875 (nec 1859), which they found in the fæces of patients suffering from intestinal disorders. The organism is described by them as being pear-shaped and 10 µ to 15 µ in length and 3 µ to 4 µ in breadth. The posterior extremity terminated in a point (fig. 17).
Fig. 17.—Trichomonas intestinalis, Lkt. (After Grassi.)
A row of twelve or more cilia was said to commence at the anterior end and extend over the body. Leuckart stated that this parasite, placed by the two authors in the genus Cercomonas, was a Trichomonas, and that they mistook the undulating membrane for cilia, and overlooked the flagella. Notwithstanding its striking similarity with T. vaginalis, it was said to be distinguishable from that species by differences in the undulating membrane. Lambl’s C. intestinalis38 (of 1875) which corresponds with C. hominis, Davaine39 (1854), is regarded by Leuckart as a true Cercomonad (characterized by a flagellum and the absence of an undulating membrane, see p. 61), and is thus generically distinct from Trichomonas.
The correctness of Leuckart’s judgment in regard to Marchand-Zunker’s flagellate was demonstrated by Grassi’s researches, accounts of which were published soon after. In about 100 cases of bowel complaints in North Italy and Sicily, Grassi found Flagellata in the stools, which he first named Monocercomonas and Cimænomonas, but later termed Trichomonas. However, in opposition to Leuckart, Grassi has also classified Davaine’s C. hominis (= C. intestinalis, Lambl, 1875) as Trichomonas, and most authors have followed his example. Hence arose the use of the name Trichomonas hominis. It was through Janowski (1896) that the former view was again taken up. After a review of the literature, the occurrence of Cercomonads in the intestine of human beings in addition to Trichomonads was considered by the author to have been proved, and he added a description of the Trichomonads. According to this, all morphological distinction between T. vaginalis, Donné, and T. intestinalis, Leuckart, disappeared. On the other hand, it is worthy of note that the smaller size, the more pear-shaped form, and the longer flagella differentiate T. intestinalis (= T. hominis) from T. vaginalis.40
Fig. 18.—Trichomonas intestinalis from man, showing anterior flagella, cytostomic depression anteriorly, undulating membrane, nuclei, and axostyle. ×2,500. Original.
The easily deformed pear-shaped body has three free flagella anteriorly, and an undulating membrane with its flagellar border terminating in a short free flagellum