ix ATTENUATED FORMS OF SMALLPOX 97 



was not then fully understood, in spite of the enlightened 

 practice of Haygarth, and of Waterhouse and others in 

 America. The deaths from smallpox in London actually 

 continued to increase and attained a maximum after the 

 introduction of inoculation. But towards the end of the 

 century the mortality declined, and was sensibly less before 

 vaccination was introduced. After the latter event the fall 

 in the death-rate was rapid, and in our own time although it 

 still fluctuates it has nearly reached zero. The general 

 improvement of health from other causes must of course be 

 taken into account. 



It was further objected that many of the inoculated cases 

 were severe and some fatal, and lastly that the operation was 

 not invariably protective. It must however be borne in mind 

 that the experience of Dimsdale, Adams and others shows 

 that the risk could be reduced with due care and skill almost 

 to vanishing point, and that there is no such thing as absolute 

 protection ; which is conferred neither by vaccination nor by 

 any other prophylactic method, nor even by a previous attack 

 of the disease. Upon the whole Sir Thomas Watson's opinion 

 seems to be justified, that the advantage derived by the 

 individual from inoculation was counterbalanced by the 

 increased risk to the community. 



Inoculated smallpox and vaccinia appear to be essentially 

 modifications of smallpox, altered by transmission through 

 man or animals. Dr. Copeman has indeed demonstrated 

 by experiment the intimate relationship of the three disorders, 

 which he thinks are probably descended from one common 

 stock. The mild inoculated disease has become attenuated 

 in passing through the human system by the way of inocula- 

 tion. In this process the virus is introduced amongst the 

 epithelial cells of the tissues, where it sets up a free local 

 growth ; and it appears, according to our present knowledge, 

 that the spores or parasites lose certain of their properties 

 when they enter the system in this way. When smallpox is 

 acquired in the ordinary manner, presumably by the air-borne 

 parasites entering the air passages, those which succeed in 

 overcoming the leucocytes and entering the tissues produce 

 the more severe disorder. The attenuation of the virus in 

 inoculated smallpox may also be due in part to a higher 

 degree of immunity present in the subject in whom the 

 inoculation is made ; for it may be assumed that the average 

 immunity of those inoculated is higher than that present in a 

 person taking smallpox in the ordinary way. Vaccinia is 

 probably derived from the mild inoculated disease, further 



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