Whilst the susceptibility to the ordinary mode of infection is very general, varicella can probably not be transmitted by inoculating healthy, susceptible children; so that the contents of the varicella vesicle and variola pustule differ essentially. At any rate the inoculation succeds only exceptionally under especially favorable, and to us unknown, conditions.
Numerous inoculation experiments were tried during the first half of the last century partly for purposes of differential diagnosis and partly to demonstrate the difference between variola and varicella. (For literature until 1829 see Hesse). The results were generally nega tive and the exceptional successes consisted in a generalized exanthem and not in a localized vesicle at the site of inoculation.
It is certain in all inoculation experiments that the contents of the varicella vesicles cannot cause smallpox either in vaccinated or un vaccinated individuals One attack usually confers a lasting immunity and exceptions are exceedingly rare. Just as there are individuals who obtain an unusually high grade of immunity through an attack of varicella with marked intoxication symptoms, so on the other hand there are those who get but a slight immunity from a very mild attack and may, therefore, have a second attack These are hardly to be considered under the ordinary rule, however, as the second attack follows closely upon the first. In the older literature instances are found in the writings of Heim, iliifeland, Canstatt and Trousseau and in the more recent publications of Comby, Blair, Butler, Netter, etc. The interval has been as follows: fourteen days (Vetter, 1860), ten days (R. Neale, 1891), nineteen to twenty-two days in four eases (Dawes, 1903). Kassowitz saw a patient who had two severe attacks with an interval of one and a half years, and Gerhardt treated a child who had three attacks.
The susceptibility is not influenced by the occurrence of other diseases. Varicella may be present at the same time as some other disease or may immediately precede or follow it. Varicella is easier to tell when it occurs with some other acute infection on account of the vesicular eruption being much more easily distinguished from measles, scarlet fever or rubella than these are from one another.
In the older literature there are numerous examples of the occur rence of one or two infectious diseases at one time with varicella (le Roux, Reuss, Boehm, cited by Hesse) and in the more recent times the following may be cited: Thomas (1S71), Fleischmann (1570), Prior (1SS3), Lichtmann (1S92), (1895) Netter (1594), Bery (1898), Heubner (1904), and others in French and English literature cited by Cerf. Observations of this kind arc rare when confined to pri vate practice but in children's hospitals such occurrences are not at all uncommon.
The relation of scarlet fever to varicella is of interest and the scarlet fever virus may enter through a varicella pustule. Heubner (1903) noted that when scarlet fever attacked a chicken-pox patient the ness spread from a scratched pustule just as it would from a wound.
Pospischil (1904) gathered from his large material that scarlet fever attacked varicella patients particularly in the first stage when the new vesicles were making their appearance. Ile believes that. the majority of general streptococcus infections following measles and varicella are due to infection with scarlet fever. Cerf (1901) has noted that nearly all the varicella that follows scarlet fever is attended by suppuration. Of much more importance, however, is the simultaneous occur rence of varicella, variola and vaccinia, or of the immediate sequence of the same, because the independence of varicella is thus noted. The onset of varicella during or immediately after vaccination is of frequent occurrence. It may be noted at the time of vaccination. Varicella may appear at the same time as variola. Whilst Thomas (1874) neither saw nor believed in this, we have nevertheless a number of unprejudiced observations. Bourland (1894) saw both diseases during a double epi demic and Pages (1902) the simultaneous occurrence of variola, vari cella and vaccinia. J. F. Schamberg (1902) saw a case of varicella brought into a smallpox hospital and the disease developed in 33 chil dren with variola. In some eases only seventeen days elapsed between the appearance of the two eruptions. Where the idea of the identity of the diseases prevails and patients with varicella are isolated with smallpox cases, unless the former have been protected by vaccination they will have an attack of smallpox (Lothar Meyer, Steiner, Forster, Quineke, Fleischman, Eisenschitz and others).
Vaccination takes in children who have had chicken-pox and runs the same course as in those who have not had it,—a fact which any physician can easily verify, and there are numerous references to this in the literature of the last half century.
The accidental occurrence of varicella or variola during the course of the disease has a practical significance.
We will now consider the reasons why the two diseases are not identical. As has already been stated, some physicians believe that the two diseases are only differences in intensity of a single disease. We have not room to consider in detail the century long discussion hut will give only the important facts which show that the view of the dualists is correct. One should remember that in many of the discus sions the views of the dualists were not always correct and some of their claims were not based upon sound observations.
1. Inoculation with the contents of the varicella vesicle always produces varicella and never variola.
2. The occurrence of varicella does not protect from variola or vaccinia and the reverse is also true.
3. The third question which has been discussed at great length is whether a patient with varicella can cause variola in another and this may he answered in the negative.
Varicella is a disease etiologically different from variola but which at times has clinical manifestations greatly resembling smallpox.