It would serve no good purpose, and is not within the intended scope of this paper, to describe at length and minutely the diagnostic marks of true vaccinia. The object is rather to impress upon the reader the serious fact, that vaccination is an event of weighty significance, the influence of which is of such consequence that a large portion and perhaps the whole of his life will be affected by it. The simplicity of the operation, and the inconsiderable illness which usually succeeds it, should not blind any one to the fact, that it is an event of deep concern to every individual. It is not the trivial thing which many regard it, to be ignorantly or negligently performed and with uncertain effect.

HOW OFTEN SHOULD VACCINATION BE REPEATED?

The subject of re-vaccination is one upon which much difference of opinion exists in regard to some minor questions. But upon the importance of it, and the use of it, as a general rule of practice, there is great unanimity of opinion.

Why is re-vaccination necessary?

There are two essential causes for it; one is, because the primary vaccination was defective.

Jenner recognized this necessity, and he was accustomed to do what is altogether too much neglected now, that is, to watch the vaccinations throughout their entire course, and if any irregularity occurred, to advise re-vaccination immediately, or at some early convenient period; because he had already learned that such vaccinations were not fully protective and could not be depended upon as security against small-pox.

In these latter times, when negligence, ignorance, or defective lymph so frequently vitiate the results of vaccination, this cause for a re-vaccination is vastly more common than in its early history.

It is the more unfortunate that it is so because the primary vaccination, if it has taken, but taken badly, will often prevent the success of a re-vaccination. And so a child who has had only a spurious vaccination is only partially, if at all, protected from small-pox, and yet is prevented from securing the protection which a good primary vaccination would have afforded.

This is another and a very important reason why the primary vaccination, at least, should always be performed only by a competent and careful operator. An imperfect primary vaccination is a very great misfortune. Re-vaccination cannot be relied upon to

make good the defects of a primary vaccination, although it is the best means of remedying the evil which can be employed. Another defect of primary vaccination is due to the application of too minute a quantity of vaccine lymph, the operation being perfect in other regards.

Dr. Marson, who was for many years physician to the London Small-Pox Hospital, shows, by an "analysis of his cases, that the mortality in post-vaccinal small-pox bears a very distinct relation. to the quality and amount of the vaccination as evidenced by the number and character of the vaccine scars. His analysis showed. that, of patients with one cicatrix over 9 per cent. died, of those with two marks 6 per cent. died, with three about 3 per cent., and of those with four and more only about 1 per cent. It showed, also, that in cases with good cicatrices less than half the number died than died among patients with indifferent marks."

This evil is largely obviated by the recent method of vaccinating, which is by abrading a portion of the skin and applying the virus to the raw surface. This pretty uniformly secures the application of the lymph over as large an absorbing surface as would more than equal the two, three, or four punctures that used to be made in inserting the virus. So that a vaccination by the modern method is generally equivalent to three or four punctures by the old method. The other reason why re-vaccination is necessary is that experience has determined, beyond a doubt or question, that, in addition to those who are only partially protected by reason of irregular or spurious primary vaccination, there is another class of no inconsiderable numbers, who, notwithstanding perfect primary vaccinations, have gradually acquired a renewed susceptibility to the contagion of small-pox in greater or less degree. It is not possible to distinguish this class from those who still enjoy the full protection afforded by vaccination. If such discrimination could be made with assurance it would be necessary to re-vaccinate only such as needed it. But the impossibility of knowing which, in a vaccinated community of adults, are liable to the infection of small-pox and which are not, involves the necessity of giving the means of protection to all.

Re-vaccination, therefore, is a wise proceeding, on the part of grown-up people, as affording probable needed security to such as have had defective infantine vaccinations, and as affording an additional security even to the best vaccinated, as no individual can tell whether he may be one of the great majority who are

so.

fully protected, or one of the small minority who are only partially Persons who have faint cicatrices with ill-defined characteristics need vaccinating more than those with good marks. Persons with one or two scars only need it more than those with three or four good ones.

AGE AT WHICH RE-VACCINATION SHOULD BE DONE.

Supposing the primary vaccination in infancy to have been unexceptional, the teachings of experience are, that the subject is safe until the period when the growth of the body is about being completed, the age of puberty. During this transition stage between youth and adult life, the changes in the system are attended in a small minority of persons with a partial loss of the protective power of vaccination, and that is a period beyond which a person possibly incurs some degree of risk if not re-vaccinated.

The importance of re-vaccination at this age is more urgent in proportion as the indications of a good primary vaccination are wanting. A good and sufficient primary vaccination is, as a rule, then fully protective until the age of twelve or fifteen years. The only circumstances under which an earlier repetition would be advisable are a known exposure to the infection of variola or the prevalence of an epidemic of the disease.

As to subsequent re-vaccinations, the weight of evidence is, that an adult re-vaccination with true bovine virus with positive vaccinal effect will be fully protective against small-pox for the remainder of life; or, as Dr. Martin says, the subject will be as insusceptible of small-pox as "if he or she had twice had that disease." This strong assertion it is certain cannot truthfully be made with the long-humanized virus. Its enfeebled protective power has been again and again demonstrated by the frequent occurrence of varioloid and even variola after adult re-vaccination with it.

The diversity of opinion respecting the needed frequency of revaccination is mostly due to not recognizing this difference in the protection afforded by the two kinds of virus.

When the Jennerian or long-humanized virus is employed (and it is only that which, until within ten years, we have had experience with), re-vaccinations should be made as often as every five to ten years, and especially whenever an epidemic of small-pox is prevailing. With true bovine virus a primary vaccination in infancy and a re-vaccination at puberty is all that is required.

THE AGE AT WHICH PRIMARY VACCINATION SHOULD BE PERFORMED.

This is a matter of much practical interest.

If an infant has been exposed or is liable to be exposed to the infection of small-pox it should be vaccinated at once, however young. There is the less objection to vaccinating infants of very tender age with the bovine virus, because there is no danger of erysipelas, which is the great dread when humanized virus is employed. But if there is no known risk of exposure the operation may safely be delayed until the age of three or four months, but not longer, because 'soon after this the period of active dentition begins, with its attendant irritations and frequent derangements. During this period vaccination should not be attempted except for necessity, because it might not take, or it might be rendered imperfect by the other disorders of the system, and thus impose upon the child the misfortune of an imperfect primary vaccination. So that if not vaccinated before the time of teething, it is desirable to postpone it until after that process is mostly over. This waiting prolongs, by several weeks or months, the period of exposure, during which the child must be more closely guarded, and cannot without some risk be taken even upon the street, or make journeys, or be carried in any public places.

The importance of an early vaccination is the more impressive when we remember that young children have always been the most numerous victims of small-pox. The statistics of England show that one-fourth of all the fatal cases are of children under one year of age.

CHILDREN SHOULD BE IN HEALTH WHEN VACCINATED.

This rule does not necessarily exclude many children who are sickly and feeble. Scrofula does not prevent the full development of vaccinia, nor would the latter stages of chronic whoopingcough forbid the operation, and so of some other chronic disorders, but acute febrile diseases do always. Except under pressing necessity, skin affections, particularly those of a vesicular form, as herpes, eczema, and intertrigo, should occasion the postponement of the operation until they are cured.

A careful vaccinator will always examine if there be any uneruptive disorder upon his patient, such as often is found behind the ears, any chafing in the folds of the neck or in the groins, before he operates.

The trained observing powers of Jenner early detected the interfering influence of cutaneous diseases, and he described how they prevented the full and correct reception of the vaccine influence. His rule of practice was "to sweep away all eruptions from the skin previous to inserting the vaccine lymph."

The period of weaning is an unsuitable time for this operation, for obvious reasons. It should not be performed, except under the most pressing need, during epidemics of any of the severe diseases of children. Also, except for urgent cause, during the seasons of extremes of temperature it had better be postponed.

CONCLUSIONS.

1. That the vaccinia produced by the proper inoculation of vaccine virus protects the subject as much as an attack of small-pox. 2. That wherever compulsory laws are enforced, the protection afforded by vaccination is satisfactorily demonstrated.

3. That as between the two kinds of vaccine virus now in use, viz., the bovine and the humanized, the bovine is to be preferred. (a.) Because it is fully protective, while the humanized gradually loses its protective power by frequent transmissions through the human system. (b.) Because bovine is exempt from the risk of communicating other diseases than vaccinia, while the humanized virus is liable to produce erysipelas, and in rare instances has conveyed the poison of syphilis.

4. That the vast importance of this subject, as it concerns the public welfare, forces the inquiry: If the best interests of communities do not demand that a supply of genuine, trustworthy, bovine virus should be always provided by skilled producers, under the official direction of the state or national governments?

5. That a primary infantile vaccination with good bovine virus is fully protective until the age of puberty, and that a re-vaccination at or about that time, resulting in any perceptible vaccinal effect, will be protective through the remainder of life.