“(1) That it diminishes the liability to be attacked by the disease.
“(2) That it modifies the character of the disease, and renders it (a) less fatal, and (b) of a milder or less severe type.
“(3) That the protection it affords against attacks of the disease is greatest during the years immediately succeeding the operation of vaccination. It is impossible to fix with precision the length of this period of highest protection. Though not in all cases the same, if a period is to be fixed, it might, we think, fairly be said to cover in general a period of nine or ten years.
“(4) That after the lapse of the period of highest protective potency, the efficacy of vaccination to protect against attack rapidly diminishes, but that it is still considerable in the next quinquennium, and possibly never altogether ceases.
“(5) That its power to modify the character of the disease is also greatest in the period in which its power to protect from attack is greatest, but that its power thus to modify the disease does not diminish as rapidly as its protective influence against attacks, and its efficacy during the later periods of life to modify the disease is still very considerable.
“(6) That re-vaccination restores the protection which lapse of time has diminished, but the evidence shows that this protection again diminishes, and that, to ensure the highest degree of protection which vaccination can give, the operation should be at intervals repeated.
“(7) That the beneficial effects of vaccination are most experienced by those in whose case it has been most thorough. We think it may fairly be concluded that where the vaccine matter is inserted in three or four places, it is more effectual than when introduced into one or two places only—and that if the vaccination marks are of an area of half a square inch, they indicate a better state of protection than if their area be at all considerably below this.”
SCARLET FEVER.
Scarlet Fever and Scarlatina are the same disease. It is extremely infectious, the contagium retaining its virulence for protracted periods. It occurs in epidemics at irregular intervals. During recent years the type of scarlet fever has become greatly attenuated, and this constitutes one of the difficulties of prevention, as the mild form of the disease is apt to be overlooked. The fatality per 100 persons attacked varies greatly with age. It is highest in children under four, rapidly declining with increasing age. Hence the importance of protecting children from attack in early life. Two results follow from the wise precautions taken to prevent attack early in life. (a) With each successive year of life the liability to attack, when exposed to infection, diminishes; (b) the danger of the attack if it occurs and its liability to be fatal becomes rapidly less with greater age. The most common mode of infection is by contact with a previous patient. Outbreaks due to milk infected by a scarlatinal patient also occur. Infected cream has also been known to convey infection. In a milk outbreak the patients would be found chiefly among the customers of a special dairyman, the cases occur almost simultaneously, except secondary cases which may be infected from the first. The simultaneous occurrence of two or more attacks in one house, especially if the same thing happens in a number of houses should throw suspicion on the milk supply. It has been suggested that scarlet fever may originate apart from human infection, from a special disease of the cow, but the evidence on this point is inconclusive.
The duration of infection is usually reckoned until the desquamation of the skin is complete, i.e. about six or seven weeks from the onset of the attack. Occasionally it is more protracted even though desquamation is complete, infection appearing to persist in discharges from the nose and ear and in sore places inside the nostril and possibly in other parts. The period of greatest infectivity is in the earlier part of the disease, when the throat is inflamed. The common notion that the disease is most infectious during the later period, that of desquamation, is erroneous. The micro-organism causing scarlet fever has not certainly been identified. The measures of prevention are those common to infectious diseases (page [317]).