A thoroughly dispassionate review of the whole subject appears to me to warrant the following conclusions:—
1st. That vaccination, though not a perfect guarantee against small-pox, diminishes immensely the risk of its occurrence; and that by periodical revaccination, this guarantee is rendered all but absolute.
2nd. That a very large proportion of the failures of vaccination are due to its careless and imperfect performance.
3rd. That to such careless performance and to the introduction of the blood and not of the vaccine matter alone, from one child to another are due the extremely rare instances in which one special disease has been transmitted by vaccination.
4th. That there is absolutely no evidence of the transmission of scrofula, consumption, or any similar disease by vaccination.
5th. That vaccination direct from the calf appears to present some decided advantages; but it has not yet been practised for a sufficient time to admit of a comparison between its preservative power and that of vaccination from one child to another.
6th. That in either case it is expedient that vaccination be performed within the first three months after birth, so as to avoid the irritation of teething which is unfavourable to successful vaccination, and also because the disposition to those skin diseases which vaccination tends to aggravate is never so considerable before the age of three months as it becomes subsequently.
Even when vaccination fails to protect against small-pox it tends to produce a modified and so much milder form of the disease, that while one patient died out of every two in the Homerton Small Pox Hospital who had the disease naturally, the deaths were only one in four of those who had been imperfectly vaccinated, and one in forty-three of those whose arms bore evidence of perfectly good and successful vaccination.
The influence of previous vaccination often scarcely shows itself in the stage which precedes the appearance of the eruption of small-pox, the fever being often just as intense, and the general symptoms just as severe as in the unmodified disease. The difference, however, becomes at once obvious with the appearance of the rash. The pocks are always much fewer than even in mild small-pox, sometimes even not more than twenty. They never attain above half the size of the ordinary small-pox pustules; they run their course and dry off in half the time, and consequently the dangerous fever which accompanies their development in the natural disease is almost or altogether absent in the vast majority of instances.
If vaccination did no more than this it would be hard to overestimate its value, or to praise as it deserves the merit of its discoverer.