In reference to the case itself, Mr George Farrow afterwards informed me by letter that the calf was one of a herd of seven, whose ages respectively varied from four to six months. At the time of his writing (October 20th) the remaining six animals were progressing favorably towards recovery—a result which Mr Farrow attributes to the employment of inhalations of turpentine and savin, combined with the internal administration of tonics. In regard to this plan of treatment, and in reference to the source of infection, he adds:—“I should have preferred trying the inhalations of chlorine gas, but as the patients were so very young and in poor condition, I deemed it advisable to try a milder course of treatment.
“The history of the case is brief. The cattle are on a very dry and well-drained farm, but during the summer there was a great scarcity of water, and they were supplied from a stagnant pool which eventually became dry. This, in my opinion, is where the disease originated.”
Mr George Farrow’s opinion is probably correct, being in harmony with the most recent results of scientific research as made known more particularly by Leuckart. But the facts thus conveyed do not explain the whole truth; or, rather, they convey it only in a very incomplete manner. Professor Leuckart’s experiments were made with several species such as Strongylus armatus of the horse, S. rufescens, S. hypostomus, and S. filaria of the sheep, and S. commutatus of the hare. Still, as regards the strongyles, partial as the results have thus far appeared, there cannot be a doubt that his successes with several allied nematode species form a key by which we may yet unlock and expose to view the entire life-history of that specially obnoxious form under consideration, namely, Strongylus micrurus. To summarise the whole matter in a few words, Leuckart supposes that all these strongyloids require a change of hosts before they can take up their final abode in the sexually-mature state. This he infers especially because their respective embryos display characters very similar to those exhibited by Olulanus. He believes that either small mollusks or insects and their larvæ play the rôle of intermediary bearer. His experiments with the embryos of Strongylus filaria prove that these larvæ can be kept alive for several weeks in moist earth, and that whilst so conditioned they undergo a first change of skin within a period varying from eight to fourteen days. Experiments on sheep, made with these moulting larvæ, led only to negative results. Unless the following facts be accepted, the scientific position remains pretty much where Leuckart left it.
On the 22nd of October, 1875, at 1 p.m., I placed the entire egg-contents of the uterus of a Strongylus micrurus on a glass slide hollowed out in the centre. Probably something like ten thousand ova were thus brought under observation, yet only three were noticed as freed from their shells, probably as the result of accidental rupture. Two of these displayed lively movements. In round numbers the ova gave a measurement of 1/300 of an inch in length by 1/750 of an inch in breadth, whilst the free embryos measured about 1/90 of an inch long, and less than 1/1000 of an inch in thickness. The integument of the embryo displayed neither markings of any kind nor any double contour. The contents of the worm were granular throughout, these granules being crowded in the centre of the body, but scarcely visible towards the head and tail, where for a considerable space (fully 1/300″) the worm was perfectly transparent. No trace of any sexual organs or their outlets was visible. An examination of numerous eggs and free embryos obtained from near the primary bronchial bifurcations (of Mr Farrow’s specimen) yielded the same microscopic results, the only thing worthy of remark being that the embryos from the mucus seemed much more lively than those which, as I supposed, had accidentally escaped their shells.
At 1.30 p.m. I placed some free embryos in two watch-glasses, one containing water and the other saliva, and placed them before the fire. Being called away professionally I found on my return at 3 p.m. that evaporation to dryness had occurred in the interval. All my attempts to resuscitate the embryos by moisture proved unavailing, a result which, though negative, proves how little capable these embryonic creatures are of enduring desiccation. If these facts be confirmed, their practical significance is not without value in relation to the choice of dry pasturage grounds for the rearing of young cattle. I may add that whilst half an hour’s immersion of the dried embryos failed to restore any sign of life, the previous warmth and moisture had caused many more embryos to escape their shells during the time they were placed before the fire.
At 4 p.m. I passed some very rich mould through muslin. Some of this finely sifted earth I placed in a watch-glass, adding a little water to moisten it, and also numerous eggs and free embryos. In a wine-glass and also in a small jar I placed some coarse earth with water added to make thin mud, and to both of these I added, not only eggs and embryos, but also portions of the reproductive organs of the adult female worms.
On the 23rd of October, at 2 p.m., I examined the contents of these vessels. All the embryos in the vessels containing the coarse earth were dead, but several were found alive in the watch-glass containing the fine moist mould. Structurally these latter had undergone no perceptible change beyond a somewhat closer aggregation of the somatic granules.
Although the embryos in the coarse wet mud had perished, the eggs with unhatched embryos appeared to have retained their vitality. Of this fact, indeed, I subsequently obtained abundant proof; and I also satisfied myself that the death of the embryos had not resulted either from the coarseness of the earth or from excessive moisture, but from the presence of numerous shreds of the uterine tubes which I had somewhat carelessly added to the vessels. Previous experiments, conducted many years back, had indeed taught me that few if any nematoid larvæ can resist the fatal action of putrid matter, however slight the putrescence.
Having removed the offending shreds, I next placed a quantity of living ova together in the earthenware jar, and allowed the earth-contents to become much drier by evaporation before the fire. I also left others in a watch-glass, which was placed under a bell-jar enclosing several ferns.
On the 25th of October I removed particles of the moist earth, altogether weighing about two grains, and, on submitting them to microscopic examination, had the satisfaction to observe about a dozen living embryos, some of which exhibited very lively movements. There was not the slightest indication of putridity; nevertheless, I noticed several shreds of the adult worms whose presence had been accidentally overlooked, and, curiously enough, all the embryos subsequently removed from the immediate neighbourhood of these decomposing shreds of tissue were almost motionless and apparently in a moribund condition. On examining the contents of the watch-glass placed under the fern shade, I noticed several points of interest. First of all the earth contained strongyle embryos, such as I had seen before. Secondly, the surface of the mould was being traversed by three or four briskly-moving Thysanuridæ, hunting about with all that restless activity which Sir John Lubbock has so well described. Thirdly, in marked contrast to the behaviour of these I noticed several slow-moving Acaridæ, apparently also employed in searching for food. And lastly, while thus engaged, the surface of the mould in the centre of the deep watch-glass was suddenly upheaved, by which I was at once made aware of the presence of another most welcome and unexpected intruder. In short, an earth-worm had crept from the dry mould in which the ferns were growing, and had taken up its temporary abode in the soft moist experimental-earth contained in the watch-glass. When contracted, this Lumbricus terrestris was barely an inch in length. On placing it under the half-inch objective glass, I noticed a single embryonic strongyle adhering to the skin, but not firmly, and evidently only in an accidental way, so to speak. It was clear to me that it possessed neither the intention nor the power to penetrate the chitinous integument of the earth-worm.