It was maintained by Dr Jenner, that this disease is never of sporadic origin in the cow, but is derived from a disease of horses called the grease, by the application of the thin secretion yielded by that disease in its earlier and less con spicuous stages. Several presumptive evidences of this connection are given by him. Some experiments made by subsequent observers gave a different result. Negative evidence, however, is less to be trusted than that which is positive ; • nd we have the respectable authority of Dr Loy for believing, that this matter is capable of communi cating the true disease to the cow, and through it to the ' human system ; nay, that without passing through the cow, the virus taken from the horse at a particular stage of the disorder, imparts the real cow-pox to the human subject. Whether it ever originates in the cow independently of the horse, is a question of more difficult solution, as all the outbreakings of contagious diseases are enveloped in some obscurity.
In the cow, the disease appears in the form of irregular pustules on the teats. At their first appearance they are commonly of a palish blue, or rather of a colour somewhat approaching to livid, surrounded by an erysipelatous in flammation. These pustules, unless remedied by caustic applications, or other effectual means, degenerate into tedious and troublesome phagedenic ulcers.
This disease is transferred to the hands and wrists of the persons employed in milking. It appears in the form of blisters, similar to those which arise from burning. Their shape is circular, where the situation will admit of it. Tu mours are formed in the arm-pits. Various febrile symp toms arise, as shivering, pain of limbs, vomiting, headach, and delirium, which continue for several days.
When communicated by inoculation, this disease as sumes a milder aspect, partly in consequence of the mat ter being less extensively applied, and partly in conse quence of the parts in which it is inserted being less dis turbed, and having a thinner cuticle than the hands. The inoculated cow-pox is much more regular in its appear ances than the casual. About the third or fourth day, a small red spot appears in the punctured part, which gra dually becomes more florid, and is slightly hardened and swelled. On the fifth or sixth day, this spot is converted into a small white vesicle. In two days this is much in creased in size, and generally acquires a diameter of one third or one-half of an inch. It has elevated edges, and, in the centre, a small depression, which is soon surrounded with a narrow crust. This last circumstance has been
ascribed to the artificial puncture ; but we have found a similar appearance in those rare cases in which inoculated ve sicles arise besides that which is formed at the noculated part. On the eighth or ninth day, a circular inflammation appears at ound the vesicle, which increases for three days, and is sometimes half an inch, sometimes two inches, in diameter. On the eleventh or twelfth day, this inflam imoion begins to lisappe.ar, first at an intermediate place between the vesicle and the outer margin of the rid a•eola, modu,ing the t,ppearance of two fleri:1 concentric rings, one in contact with the vesicle, and anothci at a distance, like a lunar bah). The becomes harder, and of a ci,uk brown coiuttr, al.d, after the ih0anunauon is gone, is converted into a horny crust, w hick atlete's tor a time, and afterwards separates, leaving a red raw-looking de prvssion, which continues to be distinguishable through being either somewhat dept esscd, or merely of a whiter colour than the neighbouring shin.
The appearances are subject to some slight varieties.
of these is a copious eruption of minute papulx on the inoculated about the third day. This goes off to a few (lays. It arises 1,001 some peculiar irrita bility in tha inoculated subject, and is not generally found to luing after it any disadvantages.
In some instances. a copious pustular eruption has a p peiled over the w !tole body, which has given rise to inter esting discus,iobs. These chiefly occurred under the practice of Dr Woodville, at the small-pox hospital in Lon Ilan, and hence w ere ascribed to some influence or yarioluus mattcr, or a v..tiolatccl atmosphere. They are, with gt eat er probability, considered by Mr Bryce as cases of true small-pox. \Ve have, however, seen two cases of general eruption, one of which was copious, and the vesicles, though smaller than that which usually arises at the inocu lated part, were distinguishable from those of small-pox by a minute central, and apparently depressed crust, which resembled the vaccine vesicle. From one of these, matter was inserted in the arm of another child, and produced the real cow-pox. Such cases, however, are extremely rare. The greater part of those in which pustules appear over the body, ale cases in which the infection of small-pox has been received into the system previously to the inoculation, has been silently operating, and at last shown its symptoms in this form. Matter taken front such pustules for inocu lation has, accordingly, produced the true small-pox.