Even when humanized lymph is made use of, the process is occa sionally retarded. This may be the case when dried lymph is employed, and is invariably seen if the patient happen to be incubating measles or scarlatina. Sometimes, too, it appears to be owing to a constitutional peculiarity. Mere retardation does not, however, affect the value of the result if the development of the induced disease be normal. Instead of being retarded, the process may be accelerated ; but this, again, is imma terial, provided the course of the pock be regular. If, however, for what ever reason, the course of the disease be not regular, and the pock be in any way incomplete, the result must be looked upon as unsatisfactory, and the protection so afforded cannot be relied upon. Vaccination is apt to be rendered irregular by the presence of acute febrile disease ; of diarrhoea ; or of certain skin diseases, especially herpes, eczema, intertrigo, lichen, and strophulus. In all such cases, directly the child's health is restored, the operation should be repeated. Unfortunately it will then often fail ; for after a spurious vaccination the child may be left—tem porarily, at least—insusceptible to the action of the lymph.
In cases of revaccination the result is often irregular. The whole process is then hurried. The papule appears early; the vesicle is fully developed by the fifth or sixth day ; and then at once declines. On the eighth day a scab forms, and becomes detached a day or two later ; so that in less than a fortnight the disease has run through all its stages. With this, the constitutional symptoms are more severe, and the itching and local discomfort greater, than in cases where the inoculation is prac tised for the first time.
Pl'oteetive Value of Vaccination.—Effectually performed, vaccination is, in the majority of cases, a permanent protection against small-pox ; that is to say, the protection afforded by it is as great as that furnished by an actual attack of variola. Jenner himself never claimed that it would do more than this. As a rule, an individual who has been successfully and sufficiently vaccinated is either insusceptible to the contagion of small pox, or is capable of taking the disease only in a mild and modified form.
It is, then, very important to ascertain what constitutes an efficient vac cination. This question has been answered by Dr. Marson, who found, as a result of thirty years' observation of small-pox cases in the London Fever Hospital, that while in unvaccinated persons the mortality was as high as 37 per cent., the percentage gradually diminished in exact proportion to the number and completeness of the vaccination cicatrices ; so that in persons who could show four or more well-marked scars the mortality was only .55 per cent. It should therefore be the aim of every vaccinator to produce four or five genuine well-developed vesicles upon the arm of the patient. With less than this number the vaccination, although it may be successful, cannot be considered to be sufficient, nor the protection as complete as it can be made. As a further precaution it is usual to re
vaccinate the individual after he has attained the age of puberty. Should this be unsuccessful, it is advisable to repeat the operation if at any time the person become liable to be exposed to the contagion of small-pox ; especially if upon examination of the arms he is seen to bear only imper fect evidence of a former vaccination. The protective power of vaccina tion is well seen in the following figures, kindly supplied me by my friend Dr. Twining. The cases were under the care of Dr. Gayton, of the Homerton Small-pox Hospital. Between 1871 and 1878, 1,574 children came under observation, suffering from small-pox. Of these, 211 had been efficiently vaccinated, and oue of them died : 396 had been imperfectly vaccinated, and of these 39 died : 179 were said to have been vacci nated, but bore no marks ; of these 46 died : 788 were known never to have been vaccinated, and of these 385 died. Taking the last two groups to gether, the mortality in unvaccinated children was 44 per cent. under ten years of age.
Method of Vaccinating.—The lymph used should be taken from the arm of a healthy child at some time between the sixth and eighth day of vesica tion, while the vesicle still retains its purity and transparency. After the eighth day it should not be used. The child, the subject of the operation, should be in good health. If he be poorly, especially if he be feverish, or be suffering from some skin eruption, the operation should be postponed. It was Jenner's own direction to sweep away all eruptions before inserting the lymph. This rule is a very important one, for although the vaccina tion may possibly take effect, it is more likely that it will fail, and a spurious vaccination may render the child's system insusceptible to the vaccine lymph without affording the desired protection against small-pox. Many methods of inserting the lymph are now in use. The simplest, and perhaps the best, is to make three separate punctures on each arm, inserting the point of a perfectly clean lancet, moistened with fresh lymph, sufficiently deeply to draw a little blood. In making the punctures the skin is stretched between the finger and thumb, and the point of the lancet is inclined down wards, so as to enter the skin obliquely. If fresh lymph cannot be obtained from the arm of another child, lymph stored in capillary tubes, or dried on ivory points, may be used. The dry points must be first well moistened with water, and then inserted into the punctures made by the lancet. As many should be used as there are punctures made ; and the points should be pressed down into the little wounds and allowed to remain for a minute. On being withdrawn, they should be pressed against the sides of the punc ture, so as to insure the lymph being left in the skin.