206 CONTAGIOUS DISEASES. 



man (retro-vaccination). By this process good human lymph 

 loses some of its activity, for, according to Mr. Ceely, the pheno- 

 mena in man, after vaccination with this retransmitted lymph, 

 appears later, smaller vesicles are produced, but ultimately, 

 after successive reinoculations on man, it regains its activity. 



The disease vulgarly termed " grease " in the horse, beheved 

 by Jenner to be the origin of variola, has nothing to do Avith 

 small-pox or cow-pox ; but it is placed beyond a doubt that the 

 horse is subject to a true equine pox, and that it is transmissible 

 to the cow by inoculation and cohabitation. It is stated that the 

 equine pox occurs as an epizootic when small-pox is epidemic. 

 When small-pox was raging in Edinburgh in 1872, I saw one 

 case of what I considered genuine equine pox. The animal (a 

 mare) presented signs of fever, had a slight cough, loss of appetite, 

 with costive bowels for eight or ten days before any skin disease 

 was observed. She was treated for a common cold, witli fever ; 

 but at the end of the time mentioned small pimples were ob- 

 served on various parts of her body, more particularly about the 

 shoulders and back. At first these pimples were very numerous, 

 small, and pointed ; the great majority of tliem, however, withered, 

 and a small scab fell off, leaving the skin bare of hair. About a 

 dozen on each side of the shoulders and upon the back increased 

 in size, became vesicular, and afterwards pustular. These erup- 

 tions had very much of the character of those seen in cow-pox, 

 namely, pimples increasing in size from a point to that of a horse- 

 bean, becoming vesicles in three or four days, and then pustules, 

 depressed in their centres. In about ten days, or eighteen 

 after the first manifestation of illness, dark, thick, solid scabs 

 formed on the sites of the pustules. These scabs did not all 

 fall off until fully a month had elapsed, and the hair was not 

 completely restored in two months afterwards, wdien I lost sight 

 of her. Jenner, Saccho, and others, have used equine lymph for 

 the purpose of vaccination, and human small-pox has been 

 transmitted through the horse to the cow, and so to the child 

 in the form of cow-pox. 



It has not been determined whether the small-pox poison 

 originated in man, the cow, or the horse ; whether man liad the 

 disease communicated to him from the lower animals, or whether 

 horses and cows had it from man. The origin will most probably 

 for ever remain a mystery, and we must be content with the 



