REPORT OF THE ROYAL VACCINATION COMMISSION. 679 



artificial, which confers the immunity is of the same disease as that towards 

 which immunity is conferred, that identity of disease has been considered 

 as essential to the conferring of immunity. And it has been argued that 

 it is a priori improbable that cow-pox should confer immunity from small- 

 pox, seeing that the two are different diseases. Such a purely theoretical 

 argument can have little weight against positive evidence of vaccination 

 having actually conferred immunity. If this be definitely proved to be the 

 fact, proof is thereby at the same time afforded that the theory is unsound, 

 either because a particular disease may confer immunity against a different 

 disease, or because small-pox and cow-pox are not different diseases. For 

 the practical object with which alone we are concerned, it is not material 

 that we should reach any conclusion upon the question what is the real 

 source of error in the theory alluded to, supposing it to be erroneous ? 

 We shall content ourselves, therefore, with a very brief notice of the 

 subject. 



It appears to us that we may dismiss for practical purposes the 

 theoretical questions which were discussed before us so fully. If the fact 

 be established that the introduction of vaccine matter and the consequent 

 vaccinia produce some effect upon the human body which renders it less 

 susceptible to small-pox, or which modifies that disease when the small-pox 

 virus enters the system, it will not be a strange or unwonted experience 

 that we should be unable to explain how this comes about. Science 

 has not yet succeeded in freeing therapeutics or kindred subjects from 

 obscurity, or in solving all the problems which they present. The precise 

 modus operand}, by which a previous attack of a disease furnishes security 

 against a subsequent attack by the same disease has not yet been elucidated. 

 There can be no cause for astonishment, then, if we are unable to trace 

 the steps by which vaccination exerts a protective influence, supposing 

 the fact that it does so be established, nor is it essential that we should 

 succeed in tracing them. Our inability to accomplish this does not seem 

 to us to be the slightest reason for regarding with doubt the conclusions 

 to which the facts lead us. 



Professor Crookshank, than whom no one has more strongly insisted on 

 the theoretical arguments against the protective influence of vaccination in 

 relation to small-pox, gives it as his opinion that vaccination creates a 

 transient antagonism to that disease. We understand his view to be that 

 an attack of disease can only afford protection against the same disease, 

 and that small-pox and cow-pox are not the same but different diseases. 

 We gather, however, that, in his opinion, so long as the state of antagonism 

 lasts, the person in whose system it exists is less likely to suffer from 

 small-pox than he would be if the state of antagonism were wanting. 

 This seems to us to amount in effect to the same thing as saying that 

 during that period vaccination has conferred some protection. Whether 

 the effect be to create antagonism or to confer protection, and whatever 

 difference there be between the mod tin ojtertntdi in the one case and in the 

 other, we know equally little about it. If a condition of transient 

 antagonism to small-pox is induced by vaccination, theoretical considera- 

 tions will not afford a guide of the slightest value to the conclusions how 

 long this transient antagonism will last, or how soon it will pass away. 



