A Persistent Parasite
( Originally Published 1918 )
"MANY members of the animal kingdom change their form in the course of their existence, and with the new structure adopt also a new way of living. Thus the caterpillar and the butterfly, for example, are in reality the same creature, but very different in shape and habits. The caterpillar drags itself heavily over the plant, gnawing the foliage; the butterfly, furnished with light and graceful wings, flies from flower to flower, imbibing a sugary liquor from each with its long proboscis. The cherry worm grows in the midst of the juice that feeds it; after attaining full size it falls from the tree with the damaged fruit and hastens to bury itself in the ground, there to undergo its transformation. Next spring it comes forth in the form of an elegant fly that lives on honey from the flowers and never again touches a cherry except to deposit its eggs therein, one by one. In the same way, again, the nut worm, after finishing its growth, bores a hole in the firm shell, emerges from its fortress, and buries itself for a time in the soil. There it becomes a beetle with a long proboscis, the so-called nut weevil, which leaves its subterranean retreat in the spring and takes up its quarters on the foliage of a nut tree, where it lays its eggs in the growing nuts.
"All species of animal life that change their shape act in this way. In the first half of their existence, under their initial form, they have certain habits and certain dwelling-places; in the second half, under their final form, they have habits and abodes that are quite different.
"Well, the worm that makes its home in the white cells or granules of the diseased pig's flesh is also subject to transformation. It has to change its form, but before doing so it must first change its abode. The cherry worm would never turn into a fly so long as it remained in the cherry; the nut weevil would never become a beetle if it continued to abide in the nut. Both must emigrate and hollow out a home for themselves in the earth if they would cease to be worms and become a fly in one case, a beetle in the other. In like manner, the parasites of the diseased pig would never attain their final form in the flesh that they inhabit; it is absolutely necessary for them to change their abode in order that the transformation may take place. But as they cannot leave their cells of their own accord and transport themselves to their new abode, which is difficult of access, as you will see, they wait patiently, whole years if necessary, for a favorable opportunity to emigrate."
"Where then is this new abode?" asked Jules.
"In us, my poor child, in us exclusively. The cherry worm and the nut weevil are content, for the purposes of their metamorphosis, with a hole in the sand; but the odious worm of the diseased pig must have the human body for its new homeónothing else."
"It can't be that the abominable creature really gets into us."
"It gets there very easily, and it is we ourselves who unconsciously open the door to the perfidious enemy. Some day or other the pig is killed for our nourishment. Its four legs become hams, other parts are made into sausages, its fat is tried out and stored away. All these various pork products are well salted, carefully dried, or sometimes smoked; nothing is neglected that will assure long keeping. Now in all this thorough treatment, this salting and trying and smoking, what do you think becomes of the little worms inhabiting the diseased flesh?"
"They must die, surely."
"That is where you are mistaken. They are very tenacious of life, the accursed things ! The strongest saline solution leaves them unaffected; but if some or even a great many should perish, there would always be plenty of survivors, for they are numerous beyond counting. Behold, then, our food infected with the vermin that at the first opportunity will invade our bodies. You eat a sausage the size of your finger, or a slice of ham, and the thing is done : with the appetizing mouthful you have just swallowed the horrible creature. Henceforth the enemy is with you, at home ; it will grow, develop, be transformed, and cause no end of mischief."
`But the stomach will digest it, I hope, as it would digest anything else; and the hateful intruder will perish."
"Not at all. The digestive energies of the stomach make no impression on it. It passes through quite untouched, protected perhaps by its resistant shell, and goes farther on to establish itself definitively in the intestines.
"And now all the conditions are the best possible for the worm. The situation is quiet, disturbance from without is not to be apprehended, and the best food in our power to furnish is supplied in abundance. With its double ring of hooks, each one shaped like the fluke of an anchor, the organism fastens itself to the wall of its abode and straight-way begins to develop. On its arrival it was a very short and wrinkled little worm, terminating at one end in a small round head, at the other in a spacious bladder. In a short time it will turn into a sort of ribbon that may attain the enormous length of four or five meters."
"Oh, how horrible!" cried Louis. "Can it be that we serve as a dwelling for such a guest?"
"Say rather for a number of such guests, since as a rule they are not found singly. They are commonly called solitary worms, an improper term, as you see, since there are generally several of them together. Their real name is taenia, or tape-worm, from their ribbon-like form.
"Imagine a narrow tape or band of a dull white color, a sort of ribbon of variable length that may measure as much as five meters ; imagine this ribbon almost as small as a hair near the creature's head, then broadening little by little and attaining the width of a centimeter; picture to yourself the entire length of the creature divided into sections or joints,-some square, others oblong, placed end to end like the beads of a chaplet, or, better, like pumpkin seeds strung one after another, and you will have a sufficiently good idea of the taenia or tape-worm.
"The number of these joints is sometimes as many as a thousand, and, what is more, new ones are always forming, for the taenia has the singular faculty of producing them indefinitely in a row, each one growing out of the preceding. All are full of eggs, detestable seed of the original malady in the pig, and then of the tape-worm in man. The terminal sections or joints, the oldest and ripest, become detached from time to time in chaplets and are expelled. Any pig nosing about in the excrement containing them is pretty sure to become infected from the eggs contained in these joints, for each one is the germ of a hydatid. These eggs will hatch in the animal's intestines ; and, as soon as hatched, the young worms, opening a passage for themselves here and there with their crown of hooks, will go and lodge wherever they please, some in the lean flesh, some in the fat, there to encase themselves in a resistant shell, a cell built out of the pig's substance, and there they will await the moment favorable for their emigration to the human body.
"These frequent losses in chaplets of discarded sections do not in the least impair the tape-worm's vigor; new sections grow, and the frightful length of the creature is maintained. Were it to lose almost its entire length, that would in no wise trouble it; let only the head remain, firmly held in place by `its hooks, and new joints will form until the worm is as long as ever. Until the head is got rid of there is no hope of deliverance. I could not describe to you, my children, the atrocious sufferings of a per-son afflicted with this formidable parasite so difficult to dislodge."
"You give us goose-flesh," said Emile, "with that five-meters-long worm that keeps growing again, each time stronger than before, provided its head is left."
"It must need very serious precaution," Louis re-marked, "not to be attacked by the creature."
"The precaution is very simple. Since the tape-worm has its origin in the diseased pig, let us beware of all pork thus infected. This infection, as I told you, is recognizable in the white granules abounding in the flesh, each granule being the abode of a little worm, the first form of the taenia. Raw meats, such as ham and sausage, are the only ones to fear, because salting and drying leave, if not all, at least some of these worms alive. But meat perfectly cooked, either boiled or baked, is absolutely without any danger even if infested with a multitude of these little granules, because heat of a sufficient intensity kills whatever worms they contain.
"The rule to follow, therefore, is plain: if a pig is diseased, it need not be summarily thrown away; its flesh, although of inferior quality, its lard and bacon, can very well be utilized, but care must be taken never to use any of this food without first thoroughly cooking it at a heat intense enough to destroy every dangerous germ. As for the pig itself, it can be kept from the measles by cleanliness, and especially by seeing that it eats no excrement. Every pig that wanders about and feeds on filth deposited along walls may find under its snout some pieces of taenia, swallow them with the dirty food, and thus become infected with hydatids.
"To finish this subject, I will tell you of another taenia which in its tape-worm form inhabits the dog's intestines, and in its bladder-like or hydatid stage has its home in the sheep's brain. Grass defiled by the excrement of dogs affected with this taenia receives the eggs of the expelled ripened sections. A sheep comes to browse this grass, and in a few weeks a terrible disease shows itself in the poor animal. With wild eye, driveling mouth, and heavy head, the animal turns round and round, always the same way, and falls gasping on its side. Food no longer tempts it, the blade of grass stops on its bleeding lips. All its efforts to stand up are powerless; it keeps looking for a support, especially for its head, and if this support is lacking it falls after a few turns. This strange disease is called the staggers, from the animal's tendency to turn and turn with staggering motions.
"Now if we open the brain of a sheep that has died of the staggers, we invariably find in the cerebral substance one or more limpid bladders from the size of a pea to that of a hen's egg."
"And these horrid worms in the bladder," queried Jules, "no doubt destroy the brain matter, little by little."
"They grow at the expense of the brain."
"I can well believe then, that the sheep is unable to stand."
"Each of these little bladders is a taenia in its first stage of development, and comes from the germ sown by the severed link or joint that the dog ejects with its excrement. As indisputable proof of this, if lambs are made to swallow some of the taenia links ejected by the dog, these lambs soon show themselves to be seized with the staggers, and in their brains are found the bladder-like organisms that cause the disease. The germs contained in the severed pieces of the taenia must therefore hatch in the lamb's intestines, and the worms thus brought into being must make their way, through a thousand obstacles, to the animal's brain, the only part of its body adapted to the development of the parasite."
"Then it is in the brain that the little worms grow and become bladders as large as hens' eggs?"
"It is only there that they can flourish. But these bladder-shaped worms are only incomplete beings, comparable to the larva of insects; and as long as they remain in the sheep's brain their final development will not be attained. To acquire their final form, to become taenias, tape-worms, these larva must pass into the dog's intestines. A conclusive experiment shows it. If a dog is made to take with its food some vesicular worms from a sheep's brain, the animal soon gives unequivocal signs of the presence of the taenia : its excrement contains chaplets more or less long of ripe joints. Furthermore, by sacrificing the dog so as to be able to decide the question more conclusively, one finds in the intestines the vesicular worms converted into veritable taenias or tape-worms. So the dog gives the sheep the germs that develop in the brain into vesicular worms; and the sheep gives the dog back these vesicular worms, which change into tape-worms in the intestines."
"But how," asked Louis, "can the dog become infected with vesicular worms when they are not expressly given to it with its food, as an experiment?"
"Nothing easier. The sheep affected with the staggers is slaughtered, and its head, the seat of the disease, is thrown away. The dog that finds it feasts on it."
"And there we have shepherd dogs attacked by taenia," said Louis. "Their excrement will spread the staggers among the flock."
"We must, then," concluded Uncle Paul, "as is recommended by those who have studied this subject experimentally in veterinary schools, exercise careful supervision over shepherd dogs and exclude from the flock those that are attacked with the taenia; finally, if the infection shows itself in the sheep, we must bury beyond the reach of any dog the heads of the slaughtered animals."