Part 25

=The Trichina= (Trichina spiralis).

FIG. 130.—Encapsuled Muscle Trichinæ in flesh, strongly magnified. ]

FIG. 131.—Male Intestinal Trichina, strongly magnified. ]

In the sexual condition this lives as a minute worm (male one-seventeenth, female one-eighth to one-sixth of an inch long), the so-called “intestinal trichina,” in the gut of human beings and carnivorous mammals. In this situation it brings forth living young (some fifteen hundred in number), and the multiplication is enhanced by the fact that of the very numerous trichinæ found in the gut there are, on the average, about twelve females to every male. The young trichinæ bore into the walls of the gut, and are carried by the blood-stream into the muscles. At first each little worm extends itself longitudinally in a muscle fibre, but, as it gets larger, curves and becomes spirally twisted, so that the sheath (sarcolemma) of the fibre is bulged more and more outwards. The growth of the young trichina is very rapid—an individual only ¹⁄₂₅₀ of an inch long before leaving the gut may attain the length of one twenty-fifth of an inch in fourteen days. It then grows no more, and the sheath of the muscle fibre gradually thickens to form a capsule or cyst. Later on, in about a year, lime is deposited in the capsule. The “muscle trichinæ” retain their vitality for several years. If now the host of the muscle trichina is devoured by any other mammal, the capsule is digested in the stomach of the latter, and the once more liberated worm becomes a sexually mature “intestinal trichina” in a few days. The pig is the ordinary host of trichinæ, which (without the intervention of any other host) can be permanently parasitic in this domestic animal, since pigs often devour swine’s flesh. They often enough devour even their own young, and, especially in large slaughterhouses, swine are often fed with the offal of their companions. The trichinæ also spread through the body of any living being (men, rats) which eats trichinous pork. The trichinæ thus introduced cause, in the human subject, a dangerous or even fatal disease known as trichinosis. The size of this book does not permit me to describe the symptoms of this complaint in man. Pigs suffer much less from the parasite; they may even contain an enormous number of trichinæ in their muscles without being noticeably ill. Symptoms of disease, however, often appear more or less clearly. A short time after eating the trichinous meat the appetite of the pigs is bad; they appear in bad spirits; the tail straightens out, and they often remain standing with bent limbs and arched backs. There may be, in addition, pains in the abdomen, diarrhœa, and fever. Later on, when the trichinæ have settled down in the muscles, the pigs suffer from stiffness in the legs and tenderness in the loins; they often cry out in pain. After this, however, health and appetite may return, and they can be fattened. Trichinous swine therefore appear quite sound, and are slaughtered in due course. The trichinæ in the pig are found most abundantly in the diaphragm, the masticatory, eye-, and other muscles of the head, also in those of the neck, larynx, abdomen, and loins. The fore part is more infested by trichinæ than the hinder part, but in very bad cases they are found everywhere, even in the hams. Remedies: (1) The swine must be prevented, as far as possible, from taking up trichinæ, and therefore must never be given the offal from other slaughtered swine. The flesh of trichinous swine should be burnt, and not buried, lest dogs or other animals should eat it and spread trichinosis. (2) Care must be taken that no trichinous pork is eaten by human beings (microscopic examination; meat inspection). Pork (or sausages) must never be used raw or half cooked. Trichinæ are killed by a temperature of 140° to 150° F. The inside of the piece of meat must be exposed to this temperature.

Family: =Filaridæ= (Slender Thread Worms).

Elongated and thread-shaped. Round mouth. Do not infest the gut or other cavities, but the tissues of the body, chiefly connective tissue. None of the species require notice here.

Family: =Ascaridæ= (Round Worms).

Relatively shorter than the worms of the preceding family. Mouth triangular, surrounded by three teatshaped lips. In the male the hinder end of the body is usually bent in a hook-like manner. The anus is not placed quite at the hind end of the body. All the species inhabit the alimentary canal (Cf. p. 211).

=Horse Worm= (Ascaris megalocephala). Male six to eight, female twelve to seventeen inches long; sometimes occurs in great balls, causing stoppage.

=Round Worm of Cat= (Ascaris mystax). Male two to two and two-fifths, female four and four-fifths to five and one-fifth inches long; in the intestines of the cat. Ascaris marginata infests the dog.

=Pinworm= (Oxyuris curvula). Male one-fourth to one-third, female one and four-fifths of an inch long. In the rectum of the horse, causing persistent itching.

Family: =Anguillulidæ= (Eelworms).

Extremely small, thin-skinned; lay only a few relatively large eggs, which develop very quickly. With few exceptions either earth eelworms (i.e. live in decomposing organic matter or humus soil) or as plant parasites leading to characteristic diseases of wild and cultivated forms. All these parasitic forms have a “mouth spine.” This structure, found in the mouth cavity, is very sharp and pointed in front, and can be worked forwards and backwards so as to penetrate the cell walls of plants. A mouth spine is not only found in the species which infest plant tissues (several species of Tylenchus and Aphelenchus, as well as all the known species of Heterodera), but also in those forms living free in the earth which bore into the exterior of plant roots (the remaining species of Tylenchus and Aphelenchus, Dorylaimus, etc.). In all cases an eelworm, devoid of a spine, is not a plant parasite. I will only deal with those parasites by which well-known destructive diseases of cultivated plants are caused. These belong to the genera Tylenchus and Heterodera. The first remain eel-shaped throughout life, but the adult females of the latter swell out considerably and become lemon- or pear-shaped.

The =Stem Eelworm= (Tylenchus devastatrix).

Length one-thirtieth to one-fifteenth of an inch long, usually of intermediate size; the two sexes of approximately equal length. Live and reproduce in various cultivated plants (e.g., rye, oats, stored onions, hyacinths, buckwheat, potatoes, clover, fuller’s teasel) and wild plants (e.g., Poa annua, Anthoxanthum odoratum, Dipsacus silvestris, Polygonum persicaria), but not to the same extent in all. It must also be added that eelworms of which the progenitors have developed for a considerable number of generations in the same plant, are not easily transferred to another kind of plant, or at any rate do not multiply vigorously there. Eelworms, of which the ancestors have lived for many years exclusively in rye, or alternately in rye and buckwheat, do not readily pass over to seedling onions, and first only reproduce in them to a small extent. The eelworms live only in stems, branches, and leaves, never in roots. In the places where they have penetrated the plant tissues an abnormal growth in thickness of the parts involved takes place, while the growth in length is either much diminished or even entirely stopped. Also the chlorophyll disappears sooner or later from the attacked spots, and rapid death generally ensues. Since only those parts of an organ which are inhabited by a large number of eelworms swell much, it is obvious that cracks are often developed in the stems and leaves concerned. It is further easily seen that the species and constitution of the infested plants will have an important influence on the progress of the disease caused by the eelworms. But since several generations of this parasite succeed one another during the same year, the resulting malformation is usually very considerable. “Clover sickness” is probably due to this eelworm.

I will treat in somewhat greater detail the =Eelworm Disease= of rye, which is largely prevalent in Westphalia and the Rhine provinces, and had already made its appearance, in the latter at least, at the beginning of the century.

The eelworms producing the disease migrate into the soil on the ripening or death of the grain, and later on go back to the new young rye plants or to other plants in which they can live, as the case may be. It is therefore clear that (1) where this disease exists the soil is infected for a time, and (2), the eelworm disease of rye principally appears in regions where the culture of rye is carried on to excess. Germination of the seed corn goes on quite normally in infected fields, and it is only exceptionally that anything particular is noticed in the young plants of winter rye during autumn and winter. The disease appears at the beginning of spring. Some plants soon become yellow and die: others appear to grow very luxuriantly; they possess a beautiful bluish-green colour and seem very healthy; later on they develop enormously in breadth, and each separate plant covers a relatively large area. The base of the stem swells abnormally, so that the plant looks as if it bore below an onion projecting above the ground. This is caused by the lower joints of the haulm remaining very short and thickening considerably, causing the leaf-sheaths which surround the base of the stem to become thicker and broader than usual. The feeble development of roots is also characteristic. The leaves generally remain short, but get very thick; they often become wavy, and may even appear frilled. All the leaves, however, are not crumpled in this way; a few remain quite normal, while others are small and grass-like, but thick (Fig. 132). Later on, the tip of the haulm and the ear often do not come out of the leaf-sheaths; in other plants the ear may appear, but remains small and deformed as well as the rest of the haulm, while the grains which develop are small. A number of shoots, however, may develop normally and bear fruit. Badly infested plants quickly die, some at the very beginning of spring, others later.

FIG. 132.—Rye plant in the later stage of the Eelworm disease. ]

Where the disease is very bad it may easily be recognized by its characteristic distribution. A number of bare places are noticed in spring on the infected fields; round about these places still living but badly diseased plants may be noticed, and the symptoms of attack are less obvious the further one goes from the bald spots.

On the death of the rye plants the eelworms mostly travel back to the soil, but sundry eggs and larvæ stop in the dried-up remains. Rye straw may further infect a diseased field by getting into farmyard manure and being brought back again with it; for the eelworms (at any rate as eggs and larvæ) are killed neither by drying nor by the action of dung and other decaying substances. Strongly infected spots (bare patches) on an infested field are usually the places where dung containing diseased rye-straw has lain for some time. From such centres the spreading of the eelworms takes place: (1) actively by the migration of the worms, (2) passively by rain, the feet of labourers, the hoofs of horses, field implements, etc.; also (on loose soils) by the wind, which not only blows about particles of earth, but also the dried-up larvæ which are always found on the surface of the ground. As the eelworms multiply very rapidly whenever they are in the plants, and as the means of distribution are very numerous, the disease spreads with great rapidity.

Remedies.—Proper rotation; limitation of the culture of rye, growing in place of it carrots, turnips, or lupines. Now and then (but not too frequently), potatoes, buckwheat, clover, and oats may be cultivated in the fields affected, at any rate before sowing rye again. Abundant manuring, especially with sulphates of potash, ammonia, and iron. Deep cultivation of the soil, since the eelworms find no food in the deeper, damper layers of the soil, nor can they pass into the dried condition, and so must die.

=Oats= suffer from eelworms just in the same way as rye.

=Clover Sickness= is marked by short stunted shoots, and whitish rounded buds, often remaining closed; also by the whitish colour and abnormal thickening of the shoots and buds.

=Eelworm Disease of Potatoes.=—Crumpling and small growth of the parts above ground. In many cases there may even be no potatoes at all, or only small ones, poor in starch, though sometimes they may be tolerably large. On the surface of the tubers there are discoloured rotten spots, not penetrating deeply, and usually (but not always) at the attached end. These dark patches contain the eelworms.

=Eelworm Disease of Buckwheat.=—Joints of the stem for the most part much thickened, but abnormally short. In many cases a large amount of branching in the lower part of the stem, usually at a place where it bears a nodular swelling. Branches generally short. There may be twists and bends in the stem and branches. Often, but not always, the formation of flowers and fruit is stopped. The thickened parts of the stem are brittle; they contain the eelworms in their interior.

The =Wheat Eelworm= (Tylenchus scandens = T. tritici).

FIG. 133.—Ear Cockles of Wheat; the third shows the eelworm larvæ on its cut surface. ]

Length of the male about one-twelfth of an inch, of the female one-tenth to one-fifth of an inch (according to the size of the galls in which the eelworms develop). The wheat eelworm is the cause of “ear cockles,” also known as “peppercorns” and “purples.” In several parts of the ear short thick dark brown galls (Fig. 133), resembling the seeds of corn-cockle, are found instead of wheat grains. Inside the thick brown shell there is a yellowish white mass, containing hundreds or even thousands of eelworm larvæ (one thirty-first to one twenty-seventh of an inch long). These are quite dry and rigid, but gradually revive on moistening, even if the black galls have remained twenty years in the dried-up condition. When the wheat is ripe the dark-walled galls are gathered in with the crop, and in many cases are sown again with the sound grains. The brown shell then decays, and the eelworm larvæ leave the gall, travelling to a neighbouring wheat seedling, where they live between leaf-sheath and haulm, also penetrating into the terminal bud. The haulm of a wheat plant infested by many eelworms remains relatively short, the leaves are often sharply bent and have wavy margins. Wheat plants thus infested closely resemble rye plants diseased in a similar way, but are much less deformed. This is because the wheat eelworms do not reproduce till they reach the ear, and there is consequently only one generation per year, while several generations of eelworms succeed one another in the same rye plant. The eelworms quickly travel from all parts of the plants into the ears, and get into the rudiments of the flowers, causing them to swell up like bladders, and their walls to become first dark green, and then dark brown. Sixteen to twenty eelworms are present in the lowest flowers of the ear, ten to twelve in those higher up (and therefore smaller), and four to six in the topmost (smallest) ones. Soon after entering the flowers the eelworms become sexually mature, and lay eggs (600 to 1600), from which are developed the larvæ that inhabit later on the cockle-seed like galls. The disease is known in England, Germany, France, and Italy, and is especially harmful in Saxony, where it sometimes attacks a quarter of the wheat crop. Remedies: Either there should be no ear cockles in the seed corn, or else the eelworms should be destroyed in them. The infested grain may either be put through a sieve, or else soaked for twenty-four hours in weak sulphuric acid (one pint strong acid to thirty-three gallons of water), when many of the galls float and can be skimmed off, while the eelworms are killed in those which sink.