The other question is one of considerable magnitude. Does the cow-pox give effectual security to the human constitution against small-pox? That it does so in many instances, is fully ascertained. The evidences of it are innumerable, and in the indivi dual cases they are in general absolutely decisive. Ap parent exceptions, however, have occurred. Reports of these damped a little the ardour of Jenner at an early stage of his inquiries. But conceiving it improbable that nature was in this instance capricious, he laboured to dis cover the true cause of failure. He found some circum stances to have occurred in the unsuccessful cases, to which he ascribed it ; and on these he established some discriminating marks between the false and the true, the imperfect and the perfect cow-pox. He considered the occurrence of febrile or constitutional symptoms as essen tial to the complete security of the patient ; and, in this point, he was followed by Dr. Pearson and others. It roust be acknowledged, however, that this may be a source of considerable hesitation. The febrile symptoms are ac knowludged to be generally slight ; and we may believe in the existence of an influence extended universally over the system, although no such symptoms are produced. On the other hand, uneasiness, fretfulness, and febrile heat, may arise from a local disease, which acts only through the medium of sensation, or fugitive irritation. If to these circumstances we add, that a vaccinated subject is only occasionally seen by his medical attendant, and that the reports of mothers and nurses are often influenced by fancy, by carelessness, or by a wish to please—we shall find little satisfaction in trusting to febrile symptom; as affording a sure diagnosis. The world is, therefore, un der the highest obligations to Mr. Bryce of Edinburgh, who, in his treatise on cow-pox, has proposed a test of a much more ascertainable kind. It consists in making a second insertion of the vaccine matter at the end of the fifth day, from the first inoculation, and observing whether this produces a vesicle of its own, which is smaller than the first, and follows the same stages, hut with an accele rated progress, so that the atcolm stircouncling the two vesicles are formed nearly at the same time. These ap pearances will shgw that the influence of the original in oculation extends beyond the part operated on, so far as to comprehend the site of the second insertion. In or der that it may be ascertained to be universal over the system, it may be some improvement to make the second at a part of the body the most distant possible from the first. By this test, we discover in what instances the mo dification to which the system is subjected is not merely local. Where no effect follows the second insertion, we are uncertain of this fact. If a vesicle is produced, but is not modified in its appearance and progress in a man ner different from the usual course of the first insertion, we conclude that the constitution has not received the requi site change. This accordingly has sometimes happened where the first vesicle has been accidentally broken. We do not know it it is even liable to occur where the pro gress of the first vesicle is apparently regular.' If not, we should conclude that no test, besides the regularity of the local appearances, would continue to be requisite. These important points may be numbered among the de siderata of this part of pathology. It is rash to infer that this difference would have taken place in any particular instance, merely because we find the patient afterwards seized with small-pox. That a person who has" passed through this test in the most satisfactory manner never can be seized with small-pox, is a principle which ought not to be confidently anticipated, but only inferred after the amplest experience. Mr. Bryce's test is principally to be valued for the important improvement which it af fords in the investigation of the subject; and for the pleasing light which it throws on the pathology of the animal economy. With respect to the advantages which it promises for distinguishing imperfect from perfect vac cination, it is certainly, a priori, much superior to that of watching for febrile symptoms. Such symptoms might arise from the temporary commotion of a great central organ, but the phenomena which occur in that test evince an important change in the dispositions of the most minute fibres in which the functions of secretion and assimilation are active.
The occasional alleged failure of vaccination in secur ing the constitution from small-pox has been snmetimes thought to arise from "the manner in which the opera tion has been 'performed." if this were the case, we should naturally look for some definite variations of the subsequent effects, corresponding to the deviations from the best method of inoculating. But there is a looseness in the causes by which the are accounted for, which shows that something still remains to he explored.
If the vesicle, when ineffectual, were dways distin guishahle by its appearance, no dubiety could occur. It is therefore somewhat satisfactory to be told, that " the spu rious pustule is more elevated and opake than the genuine, and more rapid in its progress ; that it is not cellular, nor surrounded with a distinct circumscribed areola, nor con verted into a dark shining scab." If these appearances
are observed to take place, we, of course, put no confidence in the preventive power of the affection induced. But it would be more satisfactory to have a precise knowledge of the causes even of this variation. These caus,s, how ever, are merely enumerated in a mass. Such a pustule is said to occur instead of the genuine cow-pox,"i,p those who have had the small-pox ;"—it is said to be • produc ed by blunt or lancets ;—by matter taken from a spu rious pustule—or from a genuine pustule at too late a pe mod—or by matter which has been too long kep:—or dri ed before a fire." (See tne article Cowpox in Rees' Cy clopxdia, written by Mr. Ring.) All these circumstances (excepting the bluntness of the lancet) may be supposed to occasion a modification in the disease ; but is it proba ble that they air agree in the kind of modification which they produce ? A cautious inquirer will suspect that there is here some defect of observation—something presumed rather than discovered, unless numerous cases of this wonderful coincidence are minutely described; while the captious critic will exclaim, that these assigned causes are only so many hedges behind which the wary vaccina tor provides for himself a variety of shelter io case of disappointment. Tito only light in which reason and duty view them is, as so many motives for more extended in quiry. These remarks have indeed been elicited only by the explanations given of a vesicle which "carries its spurious character in its aspect " But we may derive in struction, by contemplating a specimen of that precipi tance in forming conclusions, to which the medical world is liable in other points connected with this important subject.
In order that vaccination may afford us the required ad vantages, we ought to be able to distinguish, "without difficulty," all the cases in which the constitution is se cured by it either from disease or from danger. Vacci nation has been chiefly in the hands of persons not medi cal ; for this reason, it is among these that the most nume rous failures have occurred, and room is left for ascribing the failure to some imperfection in the cases of cow-pox, which escaped the observation of all concerned, though it might have been ascertained by better instructed indivi duals. If failure takes place among those inoculated in the most approved manner, and declared by good medical authority to have had the genuine disease in the most per fect form, the necessary conclusion is. that the faculty stand in need of more accurate information.
That some such cases have occurred is admitted ; but they are declared to be extremely few : and we are justly reminded that cases of repeated natural small-pox, as well as of natural small-pox after the best variolous inoculation, have alsn occurred. The rule of security is not wholly without exception in either instance —But, are the excep tions equally infrequent in both ? This is what we, are also told on very respectable authority. Such exceptions, we are informed, appear to be more numerous than they are, only because chicken-pox occurring after vaccination has been mistaken for small-pox. There are various sorts of chicken-pox, according to the accounts given us in the writings of physicians, and all of them are mild and safe diseases, compared with the small pox. See the varying descriptions of this disease given in works of Drs. Morton, Sauvages, Van Swieten, Burserius, Hebcrden, Cullen, and Willan. Some ssert that there is arother chicken-pox, at least an illevimate small-pox of a se verer kind, not clearly described by any of the older wri Ws, and that the rare exceptions to the efficacy of vacci nation have been cases in which this form ol disease has been erroneously taken for small-pox. The general fact we have found to be, that, where parents have brought their children, apparently under small-pox, to the practi tioner who had vaccinated them, and declared them sale from that disease, he has told them that it could not pos siuly be small-pox, and must be chicken-pox. Each party continues to retain his own opinion. The parent is certain that it was sioali-pox, the vaccinator that it was chicken pox ; but, since the children have got well, the contest is not worth the maintaining, and the inoculator enjoys his triumph.—And who will deny that he is entitled to this triumph, if the children always get well ?—ls that the fact? —We believe it is, or at least exceptions to that most lin portant of all results are t:xtremely rare. However, there fore, we may in some particulars acknowledge ourselves to be in the dark regarding the minute laws of the inocu lated vaccine disease, this one fact must determine us to cling to it as a sure preventive ol all the dangers arising from small-pox. We use the word sure. not in an absolute sense, but as admitting of exceptions so rare as to be to tally unworthy ol being taken into calculation.