SECTION IV.—Part III.—Arachnida (Pentastomes, Mites, Ticks).

The Trachearian division of the Arachnida comprises a few internal parasites that attack man, and many ectozoa which are parasitic upon man and animals. The species can only be noticed very briefly.

Fig. 50.—Pentastoma tænioides. (1) Male and (2) female, of the natural size. The egg and embryo highly magnified. After Leuckart.

Pentastoma tænioides, Rudolphi.—In the system of classification adopted by Diesing, this entozoon and its allies are placed in the division Cephalocotyleen and therefore, in association with the Cestodes, with which, however, it has no structural affinity. It was long ago pointed out by Van Beneden, T. D. Schubart, Leuckart, and others, that the pentastomes were Acarine and Lernæan Arthropods; the genus being osculant between the Acaridæ and Lernæidæ. The whole subject is discussed in Leuckart’s profound memoir quoted below.

The adult Pentastoma tænioides is characterised by the possession of a vermiform, lancet-shaped body, flattened at the ventral surface, attenuated posteriorly, and marked transversely by about ninety rings (fig. 50, 1 and 2). The cephalo-thoracic segments are continuous with the body, each supporting a pair of strong retractile chitinous claws; four in all. The head is truncated, furnished with an oval mouth, armed with a horny lip. The integument of the body is perforated with numerous respiratory openings or stigmata. These are wanting in the cephalic segment. In the larval state (══ Pent. denticulatum) the body is armed with numerous rows of small, sharply pointed spines. The adult female measures from three to four inches in length, but the male is only about an inch long. The genital aperture of the female is situated at the extremity of the tail, that of the male being placed at the front part of the abdomen in the middle line. The mode of reproduction is oviparous, accompanied by a subsequent and complete metamorphosis.

In the mature condition this parasite infests the nostrils, and frontal sinuses of the dog and wolf, and also, though more rarely, the nasal cavities of the horse and sheep. In the pupal and larval states it sometimes occurs in the abdominal and thoracic cavities of the human body, but it is more frequently found in herbivorous mammals, such as the sheep, deer, antelope, peccary, porcupine, guinea-pig, hare, and rat. According to Creplin, it infests the domestic cat. In these animals and in man the young worms occupy little cysts within or upon the peripheral parts of the liver and lungs. I have occasionally found them free in the cavities of the abdomen and pleura.

In the course of the development of this entozoon, Leuckart recognises four well-marked stages. The first is that of the embryo with a boring apparatus. In the second stage, the embryo has become transformed into a motionless pupa. The third is the ordinary larval condition characterised by numerous rows of small spines in addition to two pairs of double claws. The fourth is the sexually-developed stage, furnished with a simple hook-apparatus, and without integumentary denticles. “Our Pentastomes, therefore,” says Leuckart, “exhibit two kinds of larval forms, an earlier and later one, such as takes place in other animals; this also occurs even in insects (Strepsiptera and Meloidæ), only that, in our case (i.e. in Pentastoma), both do not immediately follow one another, but are separated by a resting condition, which I have designated as the pupa stage. In choosing this name I do not mean to express a complete identity of this intermediate state with the pupal sleep of insects.”

Fig. 51.—Upper third of the body of Penta­stoma dentic­ulatum. Original.

So far as my own observations extend, the pupa, in its later stages, closely resembles the free larva; but, as Leuckart points out, the earlier stages are very different. The embryo, after encystation, repeatedly casts its skin, and during the intervals of these several successive moultings, the young animal makes rapid growth, accompanied by a series of structural changes. Passing through these it at length acquires the perfected larval state (P. denticulatum).

As regards the occurrence of this entozoon in the human body, the best account is that given by Frerichs. As quoted in my previous work from Murchison’s edition of Frerichs’ well-known clinical treatise, the German savant remarks:—“The Pentastoma is a parasite which has only recently been discovered in the human subject, but it is, nevertheless, far more common in the human liver than the echinococcus. It is devoid of clinical importance, because it does not give rise to any functional derangements. Pruner (‘Krankheit des Orients,’ 1847, s. 245) was the first who pointed out the existence of the Pentastoma in the human liver. On two occasions he found an encysted parasite in the liver of negroes at Cairo, the nature of which, however, he did not accurately determine. Bilharz and Von Siebold (‘Zeitschr. für Wissench. Zoologie,’ Bd. iv, s. 63) recognised in it a new variety of Pentastoma, to which he gave the name of P. constrictum. In Germany the Pentastoma was found in the human liver by Zenker (‘Zeitschr. f. ration. Med.,’ 1854, Bd. v, s. 224); it occurs, however, not only in this gland, but also in the kidneys, and in the submucous tissue of the small intestine (Wagner). The parasite is by no means rare with us. Zenker, at Dresden, succeeded in finding it nine times out of 168 autopsies; Heschl, at Vienna, met with it five times out of twenty autopsies; Wagner, at Leipsig, once in ten. According to Virchow, it is more common in Berlin than in Central Germany. During six months at Breslau I met with it in five out of forty-seven dead bodies. The Pentastoma-endemic in Germany is not identical with that which occurs in Egypt; the former is the P. denticulatum of Rudolphi.” This clear statement of Frerichs is valuable; but, as Murchison has also pointed out, there is some discrepancy between Frerichs and Küchenmeister’s record of Zenker’s experience. According to Küchenmeister, Zenker met with the Pentastoma thirty times in 200 autopsies.

Although from a purely clinical point of view, and speaking generally, this worm, as Frerichs says, can claim little attention, yet, as we shall see (when treating of the parasites of the dog), it occasionally proves fatal to the canine bearer. Not only so, it may even occasion severe inconvenience to the human bearer. Quite recently a remarkable instance of this kind occurred in Germany, some notice of which appeared in the ‘Medical Times and Gazette,’ Jan. 4th, 1879, as follows:

“Dr Landon of Elbing (‘Berl. Klin. Wochenschrift,’ No. 49, 1878) relates the case of a workman, aged forty-two, who soon after the Franco-German campaign of 1870 was laid up with pain in the hepatic region, jaundice, and gastric disturbance, which symptoms persisted more or less until 1874, when he came under Dr Landon’s care with an attack apparently of perihepatitis. It then appeared that since 1871 he had also suffered from severe attacks of epistaxis, which occurred often twice in the same day. The patient complained of a feeling of painful pressure in the left nasal cavity, but with the speculum nothing but a moderate degree of inflammatory swelling could be detected. Suddenly, at Easter, 1878, a parasite was dislodged from the left side of the nose by a violent sneeze, and from that moment the epistaxis has not occurred. Its cause proved to be the Pentastoma tænioides.”

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.).

Fig. 53.—Demodex folliculorum, var. ca­ni­nus. a, Fe­male; b, male. Viewed from be­low and in pro­file. Mag­ni­fied 300 diam­eters. After Mégnin.

The ectoparasitic arachnidans comprise a great variety of mites and ticks (Acaridæ and Ixodidæ) more or less proper to man, and also a number of creatures which, though hardly to be reckoned as human parasites, are apt to transfer themselves from animals to man. Little more than an enumeration of the forms is possible here. The Common Scab or Itch insect (Sarcoptes scabiei) forms the type of a great variety of arachnids, generally spoken of as different species according to the host they dwell upon. Mégnin, however, in his beautiful memoir, quoted below, regards most of the forms of this genus (found on the horse, hog, sheep, dog, wolf, and other animals) as mere varieties. In man the female Acarus burrows beneath the skin, forming galleries or curved channels, in which she deposits her eggs. The irritation produced is not alone due to these excavations, but to the presence also of a poison which the mite discharges when feeding. The Sarcoptes crustosæ of Fürstenberg, producing the Norway itch, is a variety, if, indeed, it can be called as much. Under the frightful name of Dermatophagoides Schérémétewsky two parasites found on an herpetic patient have been described as new to science by M. Bogdanoff, but Mégnin points out that these Acari are only female and young male representatives of his Chorioptes setiferus (var. bovis) respectively. In Newfoundland, Dr Le Roy de Méricourt discovered a singular species upon an officer who had come from Havannah (Tyroglyphus Méricourti, Laboulbène). It possesses enormous palpi, as in the genus Chyletus to which Robin refers it. Another ectozoon, placed by Mégnin and others amongst the lowest types of Arachnida, is the well-known Demodex folliculorum. It is a gregarious species, a dozen or more examples often being present in a single dilated hair follicle. Though disfiguring to the human face it produces little harm. M. Gruby made it out to be a very common parasite, infesting forty out of sixty persons; but Mégnin, in his brochure (l. c. infra, p. 119), shows this statement to be an exaggeration. It infests on the average not more than one in ten persons. According to Gruby, moreover, a single follicle in the dog may contain 200 of these mites, another statement which Mégnin deems unreliable. The Demodex of the dog is only a variety (fig. 53). Many other human Arachnids have been found, some of which appear to be genuine species, whilst others are accidental, so to speak. Of the former kind, perhaps we may reckon the two species discovered by Hessling (Cœlognathus morsitans and Entarsus cancriformis). Of the latter sort, those found by Busk, Simon, and Bory de St Vincent may be cited. The mite found in Simon’s case was the Dermanyssus avium, which infests cage-birds. Probably it was the same species which Bory found on a lady; but in Busk’s negro sailor the mite may have been D. gallinæ of the common fowl. Differing from the mites, proper, and also from the true ticks, are some bug-like forms called Argades. The two best known are the Miana bug of Persia (Argas persicus) and the Chinche of Columbia (A. chinche). Like their congener infesting pigeons (A. reflexus) these parasites are terrible blood-suckers. The bite of the Persian bug is so venomous as to have occasioned death. Various species of tick have been known to attack man, but the species have not been well determined. Although a human form has been described (Ixodes hominis, Koch), yet it is more probable that the species usually attacking man are the same as those known to infest the domesticated animals. In this list we may, therefore, reckon Ixodes nigra, Ix. bovis, Ix. ricinus, and Ix. reduvius. Cases in which one or other of these ticks occasioned much pain and distress are recorded by Hussem, Raspail, and Dr Cosson. Besides these there is a formidable tick well known at Angola (Ix. monbata). Its habits are like those of the common bed-bug. Severe pain comes on two hours after the person is bitten. It likewise attacks animals. The Ix. carapato is similarly troublesome in Brazil. Another very disgusting arachnid liable to attack man is the Galeodes araneoides. This large spider-like creature, two inches in length, commonly attacks camels and has an extremely venomous bite. One or more species of the dung-beetle mites (Gamasidæ) have also been known to fasten themselves on man. According to Latreille, they first get attached to the clothes of travellers, whence they pass to his body, and there shift about, producing great torment. Another disagreeable arachnid is the little harvest bug (Leptus autumnalis), which not only excites irritation during its crawling motion on the human skin, but even succeeds in burying itself near the hairs. The irritation thus produced is almost unbearable. This mite attacks various animals, especially dogs and cats. I myself once suffered severely from this species in consequence of fondling a young wild rabbit which, as I afterwards discovered, was much infested. When the parasites had reached my left arm-pit they occasioned extreme torture. I have known these autumnal spiders to produce small suppurating boils on the abdomen. I may add that Dr Tilbury Fox has brought under my notice an instance where the hexapod larva of another species (probably Trombidium cinereum) was found to have occasioned severe irritation in a child.

Bibliography (No. 38).—Alibert, ‘Maladies de la Peau,’ Paris, 1833.—Audouin, V., art. “Arachnida,” in ‘Todd’s Cyclop.,’ vol. i, 1836.—Beneden, Van (et Gervais), ‘Zool. Med.,’ 1859.—Bourguignon (et Delafond), in ‘Rec. Vét.,’ 1856.—Idem, in ‘Mém. de l’Institut.,’ 1862.—Cobbold, “Case of Leptus producing Boils,” in ‘Worms,’ p. 140, London, 1872.—Gamgee, ‘Our Domestic Animals in Health and Disease,’ Edin., 1861.—Gerlach, ‘Kraetze und Räude,’ 1857.—Hebra, in ‘Oester. Jahrb.,’ 1864.—Hering, ‘Die Kraetzmilben,’ Stuttgard, 1845.—Krabbe, “Husdyrenes paras. Mider.,” ‘Tidssk. f. Vet.,’ Rœk. 2, Bd. iii.—Küchenmeister, l. c., 1855, s. 412 (good figs.).—Mégnin, ‘Monographie de la tribu des Sarcoptides psoriques.’ (This work contains a full bibliography and numerous beautiful plates; see also Review in the ‘Veterinarian,’ Aug., 1877, p. 563).—Idem, “Mémoire sur un nouveau Symbiote (Chorioptes, Gerv.),” ‘Journ. de l’Anat. et de la Physiol.,’ 1872.—Idem, “Mém. sur un nouvel Acarien,” ibid., 1873.—Idem, “Mém. sur les Hypopes,” ibid., 1874.—Idem, “Mém. sur l’organisation et la distribution zoologique des Acariens de la famille des Gamasidés,” ibid., 1876.—Idem, “Mém. sur les métamorphoses des Acariens en général, et en particulier sur celles des Trombidions,” ‘Ann. des Sci. Nat.,’ 1876.—Idem, “Des conditions de la contagion de la gale des animaux à l’homme,” ‘Arch. générales de Méd.,’ 1876.—Idem, “Mém. sur le Demodex folliculorum (Owen),” ‘Journ. de l’Anat. et de la Physiol.,’ 1877.—Moquin-Tandon, ‘Elém. de Zool. méd.’ (Hulme’s edit., p. 302–328), 1861.—Williams, in his ‘Veterinary Surgery’ (good figs., reproduced from Gamgee’s translation of ‘Gerlach,’ &c.), 1872.