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that , we are not in all cases able to pronounce when disease is 

 continued by assimilation of the external (for instance) which pro- 

 duced it, and when disease is continued in consequence of a causa- 

 tion among the properties of the spirit, in which the primary cause 

 (the external) has no subsequent share. 



8. That some causes of disease have an assimilating relation 

 with blood is proved by the phenomena of the morbid poisons : 

 thus the matter (as is said) of sm&ll-pox produces matter endowed 

 with its own qualities; it is not that there is any relation between 

 the small-pox matter and blood, by which a similar pus is pro- 

 duced in the inoculated person, for inoculation will not produce 

 small-pox in the dead subject; but it is, that there are properties 

 in the virus which unite with the spirit, assimilate similar proper- 

 ties from blood, and these holding the same relation as their 

 prototypes with the constituents of blood, produce and ally them- 

 selves with the same secretion. The phenomena of syphilis, per- 

 haps the plague, and most or all of the causes of infections or con- 

 tagious disease, are capable of being continued by assimilation. 

 Assimilation, however, is not the only process of these causes: in 

 some part of their series of consequences they fall under another 

 department, expressed in the definition of our second class. 



9. But although assimilation, or the production of a likeness 

 from arterial blood, is sufficiently clear in the above instances, it is 

 not so in others. A person, from exposure to an easterly wind, may 

 get an attack of pneumonia. Can we say that the properties of 

 this wind, which affected the spirit, are retained or united with it, 

 and, rinding their similitude in arterial blood, produce the pheno- 

 mena of continued disease? or, if a person receives a blow in the 

 breast, in consequence of which a tumour forms, which in time 

 becomes schirrhous, can we say that the modified assimilating 

 state of the spirit, necessary to the disease, is maintained by the 

 properties originally imparted by the cause of injury? we should 

 exceed our warrant if in these and in similar cases we were to 

 pronounce an affirmative. Any argument derived from predisposi- 

 tion is here nugatory: for if it be said, these causes do not assimi- 

 late, because they do not in general produce such effects, it may 

 be replied, if they have no assimilating relation with the state of 

 perfect health, it does not follow that they should have none with 

 the state of predisposition ; at the same time their producing such 

 effects with the aid of predisposition, does not prove that they do 

 it by the process of assimilation, which we have described. 



10. When the evidence does not furnish a fair conclusion, we 

 are warranted only in defining the facts: certain causes, such as 

 those above adverted to, produce continued disease, and at the 

 same time produce their own likenesses, or similar properties. 

 Other causes produce continued disease, which remains without a 

 repetition of the causes; these latter do not obviously assimilate, 

 but they produce internal causation or progressive change, 

 which terminates in recovery or death. The nature of the 

 processes which regulate occurrences is to be further considered. 



