The identity of the microbe of variola has been much discussed. Guttmann and Grigorjew found in the lymph a coccus (Staphylococcus albus variolæ), Ruete a very motile diplococcus, and others streptococcus, but in cutaneous lesions it is very difficult to exclude such elements. Pfeiffer, Guarnieri, Van der Loeff, Wasielewski and others have drawn attention to small protoplasmic bodies (manifestly protozoa) found in the vaccine lymph, and which appear to be the infecting agents. Wasielewski cultivated these on a rabbit’s cornea to the 48th generation, and from the last successfully inoculated a calf and several children.
Funck finds this sporidium vaccinale constantly in the vaccine lymph and surrounding tissue, as a refractile, amœboid, spherical organism (spore) 1 to 3μ in diameter, and, less abundantly, a round or ovoid spore cyst 25μ. These cysts are either smooth or uneven like a raspberry, and have a single or double contoured membrane. They are easily stained with Sudan III. Examined in hanging drops they are seen just under the cover glass, not on the surface of the drops. Larger flattened bodies found in the lymph, with many included spores are manifestly epithelial cells. Copiman cultivated the organism in glycerinated collodion capsules in the peritoneal cavity of rabbits and dogs, producing zoöglœea masses staining peripherically with methylene blue, and which caused typical vaccinia in calves. He found the same elements in variola of man.
HORSE POX. VARIOLA EQUINÆ.
This was recognized toward the end of the 18th century, in the valley of the Severn, England, by Jenner, who believed it to be the origin of cowpox, but failed apparently to distinguish it from ordinary “grease”. To-day, when we must trace each case to a preëxistent one in some animal, and ignore the question of primary origin, we must still recognize that it passes readily from horse to cow, and from cow to horse, through the hands of milkers and stable-men, but that it also has the source of vaccinated persons in the families of those handling the horses. Whether it was also often derived from the very prevalent small pox in past times is doubtful, yet it appears to have been much more common about the year 1800 than it is to-day. When once started in a stable it passes readily from horse to horse, through the hands of shoeing-smiths and grooms, including of course their aprons, brushes, sponges and rubbers, and also through blankets, bandages, litter and other things on which the virus has been received. The susceptibility of the skin in the hollow of the pastern depends mainly on the frequency of chaps and abrasions, and to a certain extent on contact with the road-mud infected by other passing animals. At times the suffering animal licks the affected part, and determines the eruption on the mouth, lips and nose (see contagious pustular stomatitis). Megnin saw cases affecting the external generative organs and transmitted between the sexes by coition. (See vesicular eruption on the genitals). All such cases should be identified by inoculation.
Hertwig, as early as 1830 recorded the existence of horsepox in Berlin, where it has been seen frequently since, and noted its transmission to man. Bouley gave evidence of its special prevalence at Paris, and of the production of typical vaccine vesicles in man by its inoculation. More recently it has been frequently observed and studied by inoculation and otherwise.
Symptoms. These, whether seen in horse, cow or man, do not differ from those of cow pox, with which it may be held to be identical. The observations of Chauveau, Warlomont, and Pfeiffer that experimental infection, intravenous, subcutaneous, intratracheal (inhalation), or by feeding almost always failed to give the general eruption which characterizes small pox and sheep pox. It remains strictly local except when inoculated on other parts of the skin or mucosa. It must be added, however, that small pox or sheep pox, when inoculated successfully on the horse, as a rule remains confined to the seat of inoculation. The constitution of the horse, like that of the cow, tends to resist its virulence.
The affected horse may show preliminary febrile symptoms, but these are usually too slight to be noticed. They are followed by heat, tenderness and swelling of some part of the skin, usually in the hollow of the pastern and perhaps the back part of the metatarsal region, with more or less (sometimes extreme) lameness. On the swollen skin may be detected nodules, which may pass early into vesicles and pustules. The eruption varies, however, as developed on the comparatively hairless lips or nose, or on the densely pilous pastern.
On the lips, or other part lightly covered with hair, one can easily follow the successive formation of the round nodule, the distinct (sometimes umbilicated) vesicle, with its clear translucent straw-colored contents, and the pustule, which bursts, forming a sore, or dries up forming a dense scab, like that of cowpox.
On the heels, or on any part thickly covered with hair, the vesicle or pustule is rarely recognized, the exudate on the contrary takes place mainly on the surface, which becomes encrusted with an abundant yellowish concretion, matting the hairs together, and sometimes literally covering them. This may be very misleading to the practitioner who expects to see the succession of fully developed vesicle and pustule, and overlooking the true nature of the malady he may allow it to spread widely in a stable.
Describing his inoculation cases, Chauveau gives the following successive phenomena:—