Midland Naturalist/Volume 01/Parasites of Man (3)
Parasites of Man.[1]
By T. Spencer Cobbold, M.D., F.R.S.
In addition to the eight Costodes noticed in my previous communication, all of which belong to the genus Tæria, we find the human host liable to entertain several Bethriocephali. These are readily distinguished from ordinary tapeworms, not only by the absence of true suckers on the head, but also by the circumstance that the reproductive openings are placed on the ventral aspect of the proglottides, and in the median line. The classification of the Cestodes, as a whole, requires revision, but no zoological arrangement will stand that is not based on the examination of a large number of types. In may be that the out-of-the-way types are difficult to get at and comparatively rare; nevertheless it is just these aberrant types that are wanting to the Cestode systematist. The hard and fast line drawn between the armed tapeworms and the unarmed forms cannot be allowed to remain, since rudimentary hooklets have been found attached to the margin of the supplementary suckerlet or central disk of the beef tapeworm. Of course, as a matter of mere convenience it is very useful to separate the hooked and hookless Tæniæ, but the separation is not fitting as a primary basis of classification. In like manner the snouted or proboscis-bearing tapeworms, (Rhyncholæliadæ,) considered as altogether distinct from the tapeworms that do not possess any proboscis or rostellum, (Arhyncholæliadæ,) cannot be accepted. Of far more significance and value is the proposal that we should divide the tapeworms into two sub-orders, based on the characters of the egg-shell. This originated with Dr. Weinland of Frankfort. Thus, for the thick or hard-shelled tapeworms, he proposed the term Seleroleptidota and for thin-shelled forms the term Malacolepiidota. The eggs of the former require the action of the gastric juice of vertebrates to dissolve their shells, whilst the eggs of the latter readily hatch within the stomach of evertebrated animals, such as mollusks and insects. Quite recently, astonishment was expressed (in the pages of a scientific journal) that herbivorous animals (rabbits and hares) should suffer from the presence of tapeworm. It was evidently unknown to the writer that the larva of tapeworms (Cysticerei) are found in many other kinds of food than meat. To be sure, as Melnikow's discovery of the larvæ of Tænia rucumerina in the louse of the dog, (Trichoidœtes latus,) simply shows, "measles" are not necessarily swallowed as part of the ultimate host's food, but may be taken into the stomach accidentally. Respecting the question (raised by the President of the last meeting of the Section) as to the temperature necessary to destroy the eggs of tapeworms, I have no special information to offer, but it is generally understood that the ova of the Seleroleptidota can effectually resist the action of ice and frost. As to the limited powers of resistance to heat possessed by Cysticcrei we are now well informed, but we can do little more in this place than refer to Professor Perroncito's experiments and to the enquiries of Lewis, Tommasi, Pellizzari, Giacomini, myself, and others, as set forth in a series of articles published in the London Medical Record for 1874. Professor Pellizzari found that measles died at a temperature of 60° centigrade, (i.e., 140 Fahr.) According to Lewis, exposure of the parasites for five minutes to the same degree of heat, or even to 135° Fahr., renders the life of these parasites absolutely extinct.
Cestoda Continued.
21.—Dothriocephalus latus, Bremser.
22.—Bothriocephalus cordatus, Leuckart.
23.—Bothriocephalus cristatus, Davaine.
Although the last-named species closes the list of human tapeworms, properly so called, yet no record of the Cestoies of man can be considered complete without taking into account the occurrence of hydatids. These structures, often spoken of as bladderworms, form, as is now well known, the scolex condition of a minute tapeworm (Tænia Echinococcus) which lives in the dog. From a sanitary and professional point of view this parasite is of more importance than all the others put together, but it must be obvious that it would be out of place here to more than glance at its strictly zoological position. Every experienced Surgeon has to deal with instances of its occurrence in important organs, and probably not less than four hundred persons perish in the United Kingdom every year from this worm. In Australia and in Iceland the echinococcus disease is excessively fatal to man. The parasite is also scarcely less frequent amongst animals, although in these bearers its presence is only rarely attended with fatal consequences. Zoologically and morphologically the common hydatid is of great interest. Whilst the sexually mature worm supplies us with a form of human tapeworm altogether unique, (both as regards its size and the small number of its proglottides,) the larva, in the character of an hydatid, presents us with a type of polycephalous bladderworm which, so far as I am aware, has no parallel. The hydatid furnishes us also with a curious illustration of the extreme possibilities of tapeworm multiplication from a single germ. Starting with the postulate that the sum total of the products of a single impregnated germ or ovum fairly represents the "individual," (zoologically, so to say,) we find that whilst, on the one hand, the egg of any ordinary tapeworm begets only one Tænia, the egg of the hydatid-tapeworm is capable of producing, under favourable circumstances, several thousand tapeworms. To appreciate this truth, it is only necessary to observe that the six-hooked embryo becomes one hydatid. The maternal bladderworm may by proliferation beget daughter and grand-daughter hydatids, all of which in their turn may give rise to the formation of echinococcus heads in their interior, Separately these so-called heads represent as many tapeworms, and collectively they amount to many thousands. Thus, when a dog or wolf swallows the polycephalous hydatid and its offspring, all the loads of the colony of larvæ or scolices will becomes connected into sexually mature tapeworms in the intestine of the new host. The zoological individual, therefore, will comprise not merely one tapeworm, "-but a multitude of tapeworms. In other words, whilst the egg of an ordinary tapeworm like Tænia mediocanellata supplies a single colony or strobile of 1,200 joints, (proglottides or zooids,) the egg of the little Tænia Echinococcus supplies several thousands of colonies or strobiles, each of which is made up of three segments, without reckoning the head, this singular mode of tapeworm multiplication is also witnessed, though in a much less degree, in certain other forms of polycephalous bladderworms.
2h—Echinococcus hominis, Rudolphi.
This work was published before January 1, 1930, and is in the public domain worldwide because the author died at least 100 years ago.
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- ↑ Read before the Microscopical Section of the Birmingham Natural History and Microscopical Society, 10th April 1878. The specimens exhibited by Mr. Hughes on Mr. Cobbold's behalf were Bothriocephalus lotus and portions of B. cordatus; also part of a large maternal hydatid and one daughter-vesicle, together with a microscopic slide, showing the so-called Echinococus heads and hooklets.