VARICELLA. 613 



demic of small-pox, may take variola or varioloid ; this is in direct 

 opposition to the almost absolute protection afforded by an attack of 

 either of the latter diseases to another attack. Lastly, cases also occur 

 where children who have been vaccinated or had variola a few weeks 

 previously, are attacked by varicella. The above facts render it certain 

 that varicella is not the mildest form of small-pox, but is a disease sui 

 generis. The cases where persons with varicella are said to have in- 

 fected others with variola or varioloid, and vice versa, appear due to 

 mistaking mild cases of varioloid for varicella. The infectious origin 

 of varicella may almost always be traced; but all those infected, 

 whether vaccinated or not, are attacked by varicella, not by variola or 

 varioloid. Varicella usually occurs in more or less extensive epidemics, 

 which occasionally accompany, precede, or follow small-pox epidemics, 

 but in other instances coexist with epidemics of measles or scarlatina ; 

 varicella not unfrequently occurs sporadically also. 



ANATOMICAL APPEAKANCES. The exanthema begins as small, red, 

 distinct spots, which, after a few hours, are changed to limpid vesicles 

 of the size of a pea or lentil, by a copious serous effusion between the 

 cutis and epidermis. These vesicles have neither a central depression 

 nor a cellular formation. After a time their contents become whey-like, 

 but never purulent. Thin crusts form from the dried vesicles, which 

 fall off after a few days, without leaving a cicatrix. From the form of 

 the vesicles, the different varieties, varicellae globulosse, ovales, lenti- 

 culares, coniformes, and acuminatse, are distinguished. We often see, 

 especially when the eruption is very extensive, that, besides numerous 

 varicella vesicles running the usual course, a few filled with pus (vari- 

 cellae pustulosae) acquire the appearance of variola pustules, and even 

 leave cicatrices. Since the form of variola pustules is not specific, but 

 exactly resembles that of some erythema pustules, we should not at- 

 tach too much importance to the external resemblance of some of the 

 efflorescences in varicella to those in variola, and consequently consider 

 the two diseases as identical. 



SYMPTOMS AND COURSE. In some cases the appearance of the 

 eruption is the first symptom of the disease. Even the most careful 

 and anxious mothers often notice no prodromal stage, and assure ua 

 that, the day before the eruption appeared, the child was perfectly 

 well. More rarely the exanthema is preceded for a day or two by 

 slight fever and general discomfort, derangement, loss of appetite, 

 headache, etc. The varicella spreads over the body without any regu- 

 larity. The eruption is usually thickest on the back and breast. The 

 face occasionally remains perfectly free. Individual vesicles develop 

 in from six to twelve hours ; their contents become cloudy the second 

 .iav, and dry up the fourth. It is rare to have only a single crop of 



