Fig. 43.—a, b, Head and tail of the adult guinea-worm (magnified 10 and 18 diameters respectively); c, embryo (magnified 500 diameters). Original.
Into the anatomy of the adult Dracunculus I do not enter, but I may remark in passing, that the structure of the worm has been exhaustively treated of by Busk and Bastian. A résumé of their views is given in my introductory treatise. Carter and Leuckart have also added important details. As regards the structure and development of the young worms, I have to observe that the discovery of the viviparous mode of reproduction in Dracunculus is due to Jacobson. Nearly a quarter of a century ago I recognised the fact that the uterine organs of the adult worm almost completely filled up the perivisceral cavity, and that they were crowded with microscopic worms. Referring to this “find,” the late Sir George Ballingall, of Edinburgh, in his well-known work on ‘Military Surgery,’ recorded the circumstance in the following terms:—“The Assistant Conservator of the Anatomical Museum in our University has detected in the oviduct of an adult specimen from my collection myriads of minute and perfectly-developed (embryonic) Dracunculi. They can be very well seen with an half-inch object-glass, but their structure is best exhibited if the magnifying power be increased to two hundred and fifty diameters linear.” As already stated in my introductory treatise, these observations were made during the winter of 1853–54. In July, 1854, M. Robin made a similar statement after examining a fresh Dracunculus which had been extracted from the leg of a man by M. Malgaigne. Robin, not unsuitably, compared the worm to a double tube, one tubular sheath, as it were, enclosing the other. “The second tube,” he distinctly affirms, “is the oviduct, or, rather, that part which represents the uterus. The young still remaining in the uterus were nearly all coiled, sometimes with the tail sallying outwards, at others rolled like the rest of the body.” I have thought it only due to Robin and myself to show that from the first we were perfectly well acquainted with the fact of the “great development of the genital tube and of its close adherence to the parietes of the body.” To be sure, many discrepancies occurred in our writings, and in those of Busk and Carter. It was Bastian’s skill and good fortune to correct these errors. Thus, most of us agreed in recognising a slightly trilobed or tripapillated mouth; but Carter failed to demonstrate the existence of these tubercles, and spoke of the oral aperture as being simple and “punctiform.” The body throughout its three upper fourths appeared to me to be cylindrical, but Robin found that it was flattened. It is finely striated transversely, except at the part where it contracts to form the slender, pointed tail. According to Carter, Robin, and Davaine, the young attain a length of about 1/33 of an inch, but Bastian gives it as about 1/42″. In thickness, Carter gives the approximative diameter as 1/633″, Robin makes it 1/990″ to 1/1320″, whilst Bastian gives their breadth at 1/1428″, and Davaine at 1/2500″. I estimated their greatest length and breadth to be 1/30″ by 1/1000″. Robin and myself thought we recognised a distinct, rounded, anal orifice; and whilst Busk, on the one hand, saw nothing which in the slightest degree indicated the presence of an anal opening, Carter, on the other hand, described the structure which we called the anus as a gland, at the same time placing the alimentary outlet on one side and a little above it. According to Bastian, “the intestinal tube is about 1/87″ in length, and appears to consist of a simple canal of varying calibre, pursuing a nearly straight course, and terminating exactly at about the middle, in length, of the worm.” Like Robin, Bastian recognised œsophageal and stomachal divisions, and in a few examples he observed the cæcal or terminal portion of the intestine to be partially reflected upon itself. In regard to the circular opening which Robin and myself described as the anus, Bastian says there is a rounded body, “about 1/2200″ in diameter, with a dark or light spot in the centre, according to the varying focal distance, and which seems to represent a central aperture. Sometimes, above this, traces of two or three large cells may be recognised, whilst behind nothing definite can be made out, save that the cavity of the body is visible for about 1/400″. In other specimens of the young worm the central body and spot are wanting, but, in its stead, two lateral sacculi are met with, about 1/3300″ in diameter, that communicate with the exterior by a minute channel through the integuments, which can sometimes be distinctly recognised. At other times the channel is obscured by protrusion, which appears to have taken place through it, of a minute bilobed papilla, projecting 1/10,000″ from the side of the body. When the projections are seen, the sacculi are indistinct.”
Fig. 44.—Embryos of Dracunculus. Magnified 500 diameters. After Bastian.
As Bastian found the young in all stages of development from the germ condition 1/5000″ in diameter up to the perfect embryo, and as, moreover, he, like the rest of us, could detect no sexual orifice in the adult Dracunculus, he was led to express his belief that the young were produced agamogenetically. He went so far as to call the germs pseudova. It was with great reluctance that I dissented from the views of so gifted an observer as Bastian; nevertheless, later researches have shown that I was justified in not hastily concurring in the theory of a non-sexual mode of reproduction for Dracunculus.
Among the many advances of modern helminthology, the discovery of the true source of the guinea-worm is not the least important. To the late M. Fedschenko (the lamented and accomplished Russian traveller, who lost his life in a snowstorm on the Alps), science stands indebted for this memorable advance. Fedschenko showed that the embryos of Dracunculi, after quitting the human host, succeed in effecting an entry into the bodies of entomostracous crustaceans belonging to the genus Cyclops. Within these intermediary bearers, after twelve hours’ sojourn, the embryos undergo a change of skin, attended with subsequent growth. Here they remain to complete their larval development, which takes place within a period of five weeks, or, as Fedschenko himself told me, one month and six days. At length, as perfected larvæ, they are, together with their crustacean hosts, transmitted to the stomach of the ultimate or human bearer. It is probable that sexual maturity is next acquired within the human stomach, copulation following. After this, the females migrate to the situations in which they are found beneath the skin of the human bearer, whilst the males perish and pass out with the fæces. Thus much I gathered from M. Fedschenko himself when he visited this country, and I possess a sketch of the larvæ made by him at the time (October 23rd, 1873). One of the figures represents a larva which has undergone ecdysis, the long and narrow embryonic tail being supplanted by one which is blunt and forked at the tip. The somatic contents of the embryo have at the same time differentiated into a complete intestinal tube, and a constriction marks the junction of the œsophagus with the stomach. There is also internally an oval-shaped mass of cells near the centre of the body. These represent the commencement of the reproductive organs.
What I had gathered from Fedschenko in conversation thus epitomises that which has since been much more fully stated by Leuckart; and it is only fair to add that the Russian traveller was led up to his discovery by the previous investigations of Leuckart respecting the young of Cucullanus. The Leipsic helminthologist had, indeed, specially instructed Fedschenko as to the probable source of Dracunculus.
It is often thus that science makes its clear advances, since a master-mind is needed to set others on the right track. The embryos of Cucullanus and Dracunculus bear a close resemblance to each other, and the similarity of the types is continued on, though not in the same degree, in the next stage of larval growth, after ecdysis. The higher larvæ of both have their tails trifurcate at the tip, the head of the Dracunculus-larva being distinguished by the presence of a pair of papillæ. In the case of Cucullanus the embryos are, according to Leuckart, passively transferred to the stomach of Cyclops by the mouth; but in the case of Dracunculus, Fedschenko saw the embryo in the act of perforating the bodies of the little crustacea at the ventral surface, where the segments are bound together by a thin and easily penetrated connecting membrane. The larvæ then proceed to coil themselves within the limbs, as many as six or even a dozen of the parasites being occasionally found within the body of a single crustacean host. When they have reached full larval growth they measure about 1/25″ in length. Of course, after attaining this stage, it is a matter of conjecture as to the precise way in which their final destiny is accomplished. Fedschenko fed dogs and cats with the infected crustacea, but failed to rear Dracunculi in these animals. Clearly, these carnivora were unsuitable hosts. Could Fedschenko have experimented on man the result would probably have been very different. Arguing from what happens in the case of Cucullanus amongst fishes, and Trichina in man, there can be little doubt that all the further and final changes undergone by the larvæ are accomplished within the human host. These changes are usually, if not invariably, consequent upon a direct transference of the infested entomostraca along with water used as drink. Thus, it must at once be evident that the simple sanitary precaution of filtering water before use is amply sufficient to ensure the prevention of attacks of dracontiasis or the guinea-worm disease. The theosophical remedy of Moses against this invasion by fiery serpents, as the worms were called in his time, and the modern prophylactic measures dictated alike by science and common sense, thus stand in striking contrast the one to the other. In the nature of things it must ever remain that unreason and reason will select diametrically opposite methods of action, equally, no doubt, with the good intention of bringing about beneficial results.
From what has now been advanced, it will be seen that as regards the mode of infection the views categorically expressed in my previous work (‘Entozoa,’ p. 387) cannot be maintained. What, however, is there stated in respect of treatment still holds good in the main, even as regards prophylaxis.
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