SMALL-POX. 597 



most entirely for the rest of life, after one attack. The disease arti- 

 ficially induced by vaccinating with the cow-pock has a similar effect 

 on the predisposition. In some persons it seems to remove the ten- 

 dency to the disease for life, in others only for a number of years ; but 

 the latter class are rarely affected with severe forms of small-pox when 

 exposed to infection. Since, in our day, almost every one has been 

 vaccinated during childhood, it may be readily understood why the 

 number of cases of small-pox is far smaller now than before the intro- 

 duction of vaccination ; and since, after vaccination, any returning dis- 

 position to small-pox rarely reaches a high grade, we may also under- 

 stand why, in the epidemics of the present day, the milder forms of 

 the disease (varioloid) preponderate over the severer forms, which 

 were formerly the most common. At certain times, in more or less 

 extensive localities, from some unknown cause, the intensity of small- 

 pox poison, or the susceptibility to it, is greatly increased ; epidemics 

 result. These are more apt to occur in summer, but are not limited 

 to any season. They have a variable duration, and the cases are 

 sometimes malignant, at others very mild, although we cannot dis- 

 cover any cause for this difference. 



ANATOMICAL APPEARANCES. The anatomical changes in the skin, 

 after infection with small-pox, are those of a superficial dermatitis, with 

 a tendency to suppuration. In the milder forms of the disease, the 

 suppuration starts from the cells of the rete Malpighii only ; in the 

 severer forms, on the other hand, it attacks the tissue of the cutis, 

 destroys it, and leaves a loss of substance, which is replaced by cicatri- 

 cial tissue. It is only in the latter cases that evident traces of the 

 disease (pock-marks) remain for life. In the somewhat malignant 

 epidemic that raged in Germany last year, these extensive and 

 deep destructions of the skin, such as used to occur frequently, were 

 rarely seen. 



Variolous dermatitis commences with circumscribed hypersemia of 

 the skin, which, according to Barenspntng, extends through the cutis 

 into the subcutaneous tissue. Very soon, elongation of the papillae in 

 the efflorescence, and, more particularly, swelling of the cells of the 

 rete Malpighii, change the hyperaemic spot of skin into a sharply- 

 bounded nodule, flattened on top, which is not as yet excavated, and 

 contains no fluid, but is perfectly solid. If the process advances 

 (which is not always the case), the outer layer of the epidermis is ele- 

 vated to a vesicle by a fluid exudation. The contents of this vesicle, 

 at first clear, are soon clouded by the formation of pus-cells, which form 

 from the young cells of the rete Malpighii, and the vesicles are thua 

 changed to pustules. Besides the fluid exudation, the pus-corpuscles 

 mixed with it, and the swollen cells of the rete Malpighii (which ofter 



