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. =Chicken-Pox= is an ailment of such slight importance that it would scarcely call for notice if it were not that the resemblance of the eruption to that of small-pox sometimes leads to its being mistaken for that disease.