Chicken-Cholera.

Waikato Times, Volume XXII, Issue 1824, 15 March 1884, Page 2 (Supplement)

Chicken-Cholera.

Pui>Lic attention has again been directed to the researches of Professor Pasteur in animal inoculation with the germs of various diseases. It will be remembered that this distinguished continental scientist delivered a remarkably interesting address in the August of 1881, before the International Medical Congress, giving in outline the methods and results of his extensive and baborious experiments in this particular field. The details then given are well worthy of attention, even from a popular point of view, as showing the exactness and precision which nowadays characterise scientific investigation , they arc also in a wider sense highly important, on account of the light which they shed upon some of the obscurer diseases affecting our domestic animals. The ultimate result of these inquiries may yet be of the highest value in relation to the nature of all transmissible diseases. The investigations into the nature of ferments,, etc., carried on in the laboratory of Professor Pasteur have extended over more than a quarter of a century ; and the two more recent developments of what is technically called microbic, go far to confirm what is known up to the present time in regard to the nature of disease-germs. These two developments are described with considerable fullness in the above-mentioned address. Their chief distinguishing characteristic consists in the application of the principle of vaccination, in connection with recently discovered microscopic germs to the two diseases of chickencholera and splenic fever ; the first being a malady incidental to domestic poultry ; and the second, under various names, attacking horses, cattle, and sheep. The experiments in regard to chickencholera form a very interesting series. When the description of them is divested of a few technical expressions, the principles upon which they are conducted— as is frequently the caee in the deepest research — are singularly plain. In the blood of animals which have succumbed to chicken-cholera, there resides, according to Professor Pasteur, a collections of germs capable, under certain conditions, of almost infinite transmission. The power of reproduction possessed by these singularly minute bodies is so great, that it has been found in practice exceedingly difficult — under certain conditions, impossible — to procure the poison of the disease in a form sufficiently modified to be safely used for the purpose of inoculation. In other words, and always keeping in mind the principle of vaccination for smallpox, the smallest procurable quantity of chicken-cholera "matter," however much diluted, or otherwise apparently reduced in strength, acts on a healthy animal subject, ■when applied, so strongly as to develop the original malady in all its virulence. It is evident that with this effect, inoculation would be worse than useless, as bringing on the unmodified disease which the process was intended to avert. The method by which this scientific riddle was encountered and solved is as follows: Preparatory to what Professor Pasteur terms "virus-culture," a fowl whioh has recently died of ghicken-ebplera is made use of. The

greatest precautions are employed throughout the experiments to prevent the entrance of atmospheric germs, which might affect the results. From the body of the dead fowl a single drop of blood, as small as we please, is taken on the point of a slender glass rod, and dipped into a vessel containing a previously prepared decoction of fowl (bouillon de poulc) or clear chicken-soup. The decoction has also been beforehand rendered barren of all life by subjection to a temperature of two hundred and thirty-nine degrees Fahrenheit. This culture- vessel, with its contents thus impregnated with the single drop of contaminated blood, is then placed in a temperature of seventy- five to about ninety degrees, when, after a short interval, it becomes cloudy and dull in appearance. In reality it is swarming with tiny microbes, the merest points under the ordinary microscope, but under the most powerful instruments, resolvable into a collection of eight-shaped figures. From this first culture-vessel a single drop of the contents is again ab3traoted on the gla3S-rod point, and transferred to a second vessel of fowl decoction similar to the former one. From the second vessel, a single drop is in the same way carried to a third vessel, from a. third to a fourth, and so on. This process repeated any number of times, produces the same result in every cnlture-vessel employed — namely, a clouded appearance in the previously clear fluid, and the same signs under the microscope. After the vessels have been exposed for two or three days to a temperature of about eighty-five degrees, a sediment forms at the bottom of each and the linquid becomes clear. As, however, all impure atmospheric germs are excluded, the liquid and the deposit will remain unchanged even for months. Let us now compare the re'ative strengths of our several tinctures, as we may call them ; and, strange to say, although we would have thought that one of the more advanced stages — say the hundredth culture in direct order — would have been incomparably less fertile in germ-formation than the earlier ones, the fact is quite different. As proved by experiments in inoculation, the hundredth, even the thousandth culture is as deadly in its effects as the first one, impregnated directly from the poisoned blood. And even the blood itself used to inoculate a healthy fowl is not stronger or more certain in effect than any one of He succeeding cultures ; all are equally virulent. Would it not appear, to an ordinary experimentalist, as if the virus of this disease were thus capable of indefinite extension without being attenuated ? Perhaps so ; but not to Professor Pasteur. This most careful of manipulators discovered at last a means of modifying it. An interval of time was found to be efficacious for this purpose. The process we have described was continuously carried out ; no interval of any appreciable extent — 6nly that necessaiy for the requhed transference — elapsing between the successive cultures. This proved to be the secret of the uniform strength of the preparations. But on the other hand, supposing one hundred cultures carried out successively, and the hundred-and-firdt delayed till the expiry of a week, a fortnight, a month, or longer, then the difference was at once observable in the result obtained. The first hundred cultures continuously carried out were uniform ; the hundied-and-fiist was much less potent. Further tkan this, it became correspondingly weaker or stronger as the interval which separated it from the preceding culture was longer or shorter. It thus became practicably by varying the intervals, to prepare cultures of different drgrees of strength, until a limit was reached when the virulence became null. In this way, by using cultures for inoculation of varying degrees of strength, a certain graduated percentage of mortality amongst fowls was produced. One culture sufiiced to kill eight fowls out of ten ; another, five out of ten ; another, one out of ten ; another, none at all. It was remarkable, also, that these varying degrees of culture-strength served as starting-points from which successive series could ba produced — without allowing an interval—all of the same degree of potency as the initial one. It was found, before the actual principle of vaccination was reached in these experiments, first, that^po of the modified cultures produced, onwSbulation, a purely local disorder in the fowl Operated upon — a temporary morbid modification, which after a time passed away ; second, that the solution the virulence of which was null produced no evil effects, its own inherent reproducive power, though present, being presumed to be overcome by the natural life-resistance of the subject operated upon. But — and here we come to the principle of vaccination — when a fowl had been made sufficiently ill by a preparation of a strength which it yet had power to absorb, the most virulent culture had therefore no evil effect upon it whatever, or only effects of a passing character. It was proof for a year or more against the strongest contagion of an infected poultry-yard. In this way inoculation for chicken-cholera could be successfully performed. The " reason why " of this scientific attenuation of the chicken-cholera diseasegerms is finely explained by Professor Pasteur. " May we not," he remarks, "be here in presence of a general law applicable to all kinds of virus ? What benefits may not be the result?" The factor which intervenes to attenuate the microbe is, he concludes, the oxygen of the air. It is this which diminishes in time the virulence of the oulture, and renders it fit at last for the purpose of safe inoculation. If its culture, then, be carried on in a glas3 tube instead of in the ordinary vessel, and the end of this tube be closely sealed, the microbe will in the course of its development speedily absorb all the oxygen in the tube and in the fluid. After that, it will be destitute of oxygen. From that point, as tested by experiment, it does not seem as if any lapse of time has any effect in diminishing its virulence. " The oxygen of the air, then," Professor Pasteur remarks, " would seem to be a possible modifying agent of the virulence of the microbe in chicken-cholera ; that is to say ; it may modity more or less the facility of its development in the body of animals. So far we believe Professor Pasteur's researches and experiments to have resulted in an unquestioned success. There can be little doubts as regards chicken cholera, the most valuable and important facts are now known. — Chavibcr's Journal.