266 INFECTIVE DISEASES. 



on that subject which I hope in due time to give to the world." 

 And again in 1794, when writing in connection with this subject, 

 he adds : " Domestication of animals has certainly provided a prolific 

 source of diseases among man." 



Jenner's views were found to be incorrect, and it was shown by 

 Loy and others that the grease bears no relation to cow-pox, and 

 it is now known that Jenner mistook horse-pox for the disease 

 known as the grease. No one at the present day supports Jenner's 

 theory of small-pox in man arising from any disease of the horse. 

 Indeed, the origin of small-pox from a disease of the horse was not 

 upheld even by Jenner's pupil and nephew, Henry Jenner. The 

 latter promulgated the idea that small- pox originated from the cow. 

 He believed that small-pox, in fact, was cow-pox intensified in its 

 virulence by being passed through man. He thus expressed himself 

 " Nor may it, perhaps, be too hypothetical to suppose that the 

 cow-pox may possibly be the small-pox in its original unadulterated 

 state, before it became contaminated by passing through the impure 

 and scrofulous habits of human constitutions." The theory of the 

 origin, in animals, of human febrile diseases was, later, advocated by 

 Copland, who stated, firstly, that scarlet fever in man was originally 

 a disease of the horse, and that it formerly occurred, and had recently 

 occurred, epidemically as an epizootic among horses ; secondly, that 

 it was communicated in comparatively modern times from horses to 

 man ; thirdly, that it might be, and had been, communicated to the 

 dog. But this opinion has not been accepted, for the disease called 

 scarlatina in the horse is a lion- infectious disease, generally attack- 

 ing but one or two horses in a large stud. It neither spreads by 

 contagion nor infection ; and Williams states that it is impossible to 

 transmit it from the horse to any other animal, and that many cases 

 of the so-called scarlatina of the horse are in reality identical with 

 purpura. 



The theory was again revived, but in another form, and has 

 been adopted by the Medical Department of the Local Government 

 Board. Owing to failure in tracing, in some cases of milk scarla- 

 tina, the contamination of the milk from a human source, the 

 theory was started that in such cases the disease is derived from 

 the cow that, in other words, there is a disease, scarlet fever 

 in the cow, which is responsible for outbreaks of scarlet fever in 

 man. 



In 1882 an epidemic of scarlatina in St. Giles and St. Pancras 

 was investigated by Mr. W. H. Power for the Board. The disease 

 was distributed with a milk supply from a Surrey farm. In this case 



