localized chiefly on the face and extremities. The stiffness at the back of the neck and the retraction of the head are symptoms that do not belong to smallpox.

Septicæmia and Pyæmia.—Acute septicæmic and pyæmic conditions in which there are hemorrhagic and bullous lesions in the skin sometimes present grave difficulties in making a differential diagnosis from smallpox. In general, however, a careful elucidation of the history of the case will bring out some points that serve for differentiation.

It must be admitted, however, that the diagnosis between cryptogenetic septicæmia and hemorrhagic smallpox is sometimes impossible intra vitam. A case of this kind may be cited which occurred in New York during the epidemic last year. A woman of thirty, not vaccinated since childhood, living in a house adjoining one from which a case of smallpox had been removed, was reported to the authorities as a possible case of smallpox. It was the sixth day of her illness, which had begun abruptly with headache, backache, vomiting, and fever. On the third day of the illness there was a profuse hemorrhage from the uterus, and thereafter metrorrhagia was almost constant. On the fourth day a scarlatiniform eruption was noticed on the legs and abdomen. The rash rapidly extended and was soon interspersed with hemorrhagic points. When seen on the evening of the sixth day the patient was semi-comatose. The skin was literally covered with a dusky scarlet rash in which were noted countless hemorrhagic macules, from a pin-point to a bean in size. The conjunctivæ bulbi were chemotic, the tongue was swollen, and the fauces were deeply congested. The post-mortem examination made the following morning, six hours after death, revealed a septic endometritis, and streptococci were cultivated from the blood and the peritoneal serum.

Grippe.—An attack of grippe may simulate the early symptoms of smallpox very closely. The onset may be sudden, the muscular pains severe, the pyrexia decided, the general prostration as marked as in smallpox. In grippe, however, the muscular pains are, as a rule, more general than in smallpox, there is rarely profuse sweating, and symptoms referable to the respiratory tract soon develop, if indeed they are not present from the beginning.

Rheumatism.—The severe lumbar and sacral pains of smallpox have been mistaken for rheumatism, but such an error can be made only where the use of the clinical thermometer is unknown. A febrile movement in lumbago is absent or but slight, while in smallpox the pyrexia is usually pronounced.

Typhoid and Typhus.—Typhoid and typhus fevers have at times been confounded with smallpox. But errors of this kind can be made only where the history of the case is completely ignored. In typhus, it is true, the eruption, petechial and almost papular in character, may suggest hemorrhagic smallpox; but the eruption of typhus rarely appears before the fourth or fifth day of the illness and is located chiefly on the trunk, sparing the face. The rash of malignant smallpox develops usually on the third or even the second day of the illness and is not limited to the trunk.

Upon the appearance of the rash in a typical case of smallpox the febrile diseases with which it is most frequently confounded are measles and varicella. It is interesting to note that until the time of Sydenham, in the latter part of the seventeenth century, measles and smallpox were regarded as manifestations of the same disease, and that the Vienna school of dermatologists, even to this day, insists on the etiological unity of variola and varicella.

Measles.—As a matter of fact the early papular eruption of measles bears a considerable resemblance to the first stage of the eruption of smallpox. In both the eruption is noted first in the face. In smallpox, however, the papules have a firm, “shotty” feeling on palpation, while in measles they are smooth and velvety to the touch. In measles the eruption, viewed at a little distance, seems to present a distinctly corymbose or crescentic grouping, an arrangement which is absent in smallpox. The eruption of smallpox appears at the end of the third day, that of measles on the fourth day. The temperature in smallpox undergoes a rapid defervescence upon the appearance of the rash, while in measles it continues to rise after the eruption appears. The pronounced pain in the back is absent in measles, while the very marked catarrhal symptoms, coryza, conjunctivitis, etc., are lacking in smallpox. The subsequent course of the eruption will leave no room for doubt, since within twenty-four hours the papules of smallpox will have developed into characteristic vesicles.

Varicella.—In varicella the stage of invasion is usually much shorter than in smallpox, the prostration less marked, and the lumbar pains of the latter disease are absent. The eruption in varicella comes out in successive crops and runs a shorter course, so that lesions in various stages of development may be seen side by side. The temperature does not necessarily fall on the appearance of the eruption, and there may be a more or less marked rise with each fresh crop of vesicles, the temperature curve presenting thus a remittent character. The eruption itself presents marked differences in the character and the course of the individual lesions, as well as in their distribution. The clear vesicles shoot up from the surface, as it were, without warning; or there may be for a brief period only a circumscribed erythema like that which usually precedes the appearance of an urticarial wheal. The vesicles of varicella have usually a somewhat obtusely conical shape, while those of smallpox are distinctly hemispherical. The characteristic umbilication of the smallpox vesicle is wanting in varicella. It is true the varicella vesicle often shows a depression at its apex; but this false umbilication, as it is called, is due to the rupture of the vesicle and the escape of some of its fluid or to a partial drying of its watery contents, and occurs only after the vesicle has existed for some time. The vesicle of varicella appears much more superficial in its seat, and its roof is much thinner, so that it ruptures readily. Very moderate pressure with the finger suffices to break it. When ruptured in this way the vesicle usually collapses completely, contrasting in this respect with the smallpox vesicle, from which, owing to the multilocular character of the lesion, all the fluid does not escape.

In varicella the distribution of the lesions over the surface is far more erratic than in smallpox. The very decided tendency to grouping of lesions upon the face and about the wrists so characteristic of smallpox does not occur in varicella, in which the vesicles may appear even more extensively on the trunk than upon the face. In varicella the palms and the soles, except in infants, are almost never affected; while in smallpox these regions are practically never exempt. It is true that in the extraordinarily mild cases of smallpox, such as have constituted the majority of cases during the past two years throughout the West, lesions may or may not be present on the palms and soles; but in the severe and moderately severe cases, such as have characterized the recent epidemic in New York, the soles and especially the palms have practically without exception shown the lesions. The localization of smallpox lesions on the palms and soles deserves far more emphasis than is generally accorded it in the textbooks, many of which even fail to mention it all. It may be put down as a safe rule that a case showing an extensive eruption of vesicles or pustules, however suspicious in other respects, is not smallpox if the palms and soles are free.

Acne.—Among the skin diseases proper there are a few whose appearance upon hasty examination may occasion some confusion with smallpox. Acne