As the full-grown parasite occupies the nasal chambers of the dog, it is clear that the act of sneezing will be liable to transport the eggs and their contained embryos to the face and other exposed parts of persons who fondle dogs. In this way the germs will readily gain access to the human mouth. Ordinarily, the germs are introduced into the human stomach with uncooked vegetable food and fruits, to which they adhere after expulsion from the animal’s nostrils. The slimy nasal mucus secures this attachment, especially when it has become dry by exposure to the air. On reaching the stomach the embryos escape the egg-coverings and bore their way directly to the liver and other viscera, in which organs they become encysted and undergo the pupal transformation. Eventually they acquire a length of 2 to 21/2 lines (P. denticulatum). After a while the capsules enclosing the larvæ undergo calcareous degeneration, the parasite perishing.
In the case of dogs it is easy to perceive that when the animals are engaged in devouring the flesh of herbivora, the liberated larvæ will often come in contact with their noses. In this way contraction of the body, aided by the integumentary denticles, will secure their entrance into the nasal cavities. For our own security, therefore, we should avoid contact with dogs which frequent butchers’ shops and knackeries, and be sure that our market-garden fruits and vegetables are carefully washed before they are brought to table.
Fig. 52.—Pentastoma constrictum. Magnified four diameters. After Bilharz.
Pentastoma constrictum, Von Siebold.—This parasite is at present only known to us in the immature condition; unless, indeed, as is by no means improbable, the adult worm has been described under some other name. It was first discovered by Pruner on two occasions in negroes, and he also subsequently found two specimens of the worm preserved in the Pathological Museum at Bologna, which had been removed from the human liver. Pruner also found it in the giraffe. Bilharz afterwards frequently detected it in the livers of negroes at Cairo. It differs from the larval form of P. tænioides in not possessing integumentary spines; moreover, it is a much larger parasite. The cephalothorax is furnished with four foot-claws, and the elongated abdomen displays twenty-three rings placed at tolerably regular intervals. The anterior part of the animal is obtusely rounded off, the caudal end being conical. The worm usually attains a length of rather more than half an inch, whilst the breadth scarcely exceeds a line.
An extremely interesting account of this worm has been published by Prof. Aitken, accompanied with illustrations by Dr H. C. Gillespie, taken from specimens in the Pathological Museum at Netley. Two cases are recorded. In one of these the encysted worms were found in the liver and lungs, and in the other in the liver only. In Dr Crawford’s account of the post mortem in the last-mentioned case, Prof. Aitken quotes him as saying: “These worms varied in length from an inch to an inch and a half, and were found coiled up like a watch-spring, in small sacs scattered throughout the whole organ.” The patient was a private of the 1st West India Regiment, and died at Bathurst, Gambia, in 1854. In the other case, where the lungs and liver were infested, the patient was an African, about twenty-one years old, who had enlisted into the 5th West India Regiment at Up Park Camp, Jamaica. He had, a few months previously, come from the slave depôt at Rupert’s Valley, St Helena. According to the post-mortem report, furnished by Mr Kearney (staff surgeon), the lower lobe of the right lung contained one or two yellow specks. “When cut into, worms were seen regularly encysted in its substance.” The surface of the liver was dotted over “with about twenty or thirty yellow specks, similar to those seen in the lung.” The longest of these specimens was a trifle less than three quarters of an inch.
Whether Pent. denticulatum be or be not devoid of clinical interest, it is quite clear from Aitken’s account that P. constrictum is a formidable parasite and one that occasionally proves fatal to the bearer. As his remarks suggest, a parasite that can produce both pneumonia and peritonitis is not a creature that either the physician or the sanitarian can afford to ignore. Lastly, I must again express my belief that the so-called Echinorhynchus, described by Welch, if it be not the Pentastoma denticulatum, must either be referred to P. constrictum (in an early larval condition), or to some other hitherto undescribed pentastomatoid larva.
Bibliography (No. 37).—Aitken, W., “On the occurrence of Pentastoma constrictum in the Human Body as a cause of painful Disease and Death,” repr. from the ‘Science and Practice of Medicine,’ 4th edit., 1865.—Bellingham, in ‘Ann. Nat. Hist.,’ vol. xiv, p. 162.—Blanchard, in ‘Ann. des Sci. Nat.,’ ser. 3, t. viii, and in ‘Règn. Anim.’ (with figs.).—Cobbold, ‘Entoz.,’ p. 393 et seq.—Idem, in ‘Quart. Journ. Med. Sci.,’ 1859, p. 205.—Idem (“P. cephalophi”), in ‘Linn. Trans.,’ xxii, p. 357, and xxiii, p. 350.—Idem, in ‘Zool. Soc. Proc.,’ 1861, p. 124.—Diesing, ‘Syst.,’ i, p. 609.—Idem, ‘Revis. der Cephalocot.,’ s. 327.—Frerichs (l. c., in text), vol. ii, p. 276.—Klob (und Schroff), in ‘Gesellsch. d. Aerzte,’ Wien, 1860.—Küchenmeister, l. c., i, s. 370, Eng. edit., tab. viii.—Idem (with Van Beneden), in ‘Bullet. Acad. Belg.,’ xxii (with figs.), 1855.—Landon (quoted in text).—Leuckart, in ‘Zeitsch. f. rat. Med.,’ 1857; see also “Obs. on the development and early condition of the Pent. tænioides,” in ‘Ann. Nat. Hist.,’ vol. iii, 3rd series, 1859; also my translation of his “Further Observations on the development of P. tænioides,” from ‘Henle and Pfeufer’s Zeitsch.,’ in the ‘Quart. Journ. of Micr. Sci.’ for 1859.—Idem, ‘Bau und Entwicklungsgeschichte der Pentastomen, nach Untersuchungen besonders von P. tænioides und P. denticulatum,’ Leipzig, 1860.—Moquin-Tandon, ‘Med. Zool.’ (Hulme’s edit.), “The Linguatula,” p. 329.—Pruner (“Nematoideum”) in ‘Krankh. d. Orient.,’ 1847.—Schubart, ‘S. und K. Zeitschr.,’ Bd. iv.—Welch, see Bibl. No. [36].—Zenker, in ‘H. und Pf. Zeitschr. f. rat. Med.,’ 1854, s. 212 (with figs.).