248 



substances. It is hence to be inferred that the vital properties, 

 governing the processes of secretion, are related with chymical 

 ones existing in the blood. On this relation it is only further to 

 be observed, that we know not whether vital properties ^are directly 

 related with such chymical substances constituting the secretions 

 as are displayed in our analysis, or whether others, not known as 

 chymical properties, but in alliance with the materials of the 

 secretions, furnish the medium of a relation between the latter and 

 the functional properties of the structure. 



25. But that properties, not known as chymical, are in 

 alliance with those chymical substances exhibited by analysis in 

 the secretions, appears to be propable of them in general, from 

 this fact, that the products of secretion cannot be imitated 

 synthetically; or the result of a synthetical process, or putting to- 

 gether of such constituents as are decomposed chymically, will not 

 agree with the natural secretions in their character and relations. 

 This is true generally ; and in some particular examples the latent, 

 or those properties not known to be chymical, are the most essen- 

 tial, as in the bilious, and more especially the seminal secretions. 



26. Hence then, of secretion in general it may be said, 1. the 

 materials of the secretions are combined in arterial blood, so as 

 to be neither distinguished by the senses in this fluid, nor in gene- 

 ral to be separated from it by any known means of art; 2. the 

 secretions are separable from the blood by the agency of vital pro- 

 perties; 3. vital properties withdraw the chymical constituents of 

 the secretions from their state of combination in blood by a rela- 

 tion of affinity or of attraction, subsisting either directly between 

 the vital properties of the secretory organ and the chymical con- 

 stituents, or by a relation of affinity between the former and latent 

 properties, perhaps vital ones, in alliance with the chymical. In 

 the former case, the chymical constituents of the secretions are 

 separated by a direct relation with the functional properties ; in 

 the latter case, the relation between these is mediate. A more 

 complex mode (which is also a possible one) of the separation of 

 the secretions from the blood is, that vital properties of the 

 secerning organ pass into the blood and decompose (by relations 

 with its constituents, latent or sensible) the fluids which are 

 secreted. This mode supposes two acts of causation, which, 

 without additional evidence, it is unphilosophical to assume, when 

 the end might be accomplished by one. It supposes that one set 

 of properties pass into the blood for the purpose of decomposing 

 the secretion, and that the affinity before mentioned then operates 

 to determine the course of the separated fluid through the 

 secreting tubuli. As, however, positive evidence has been cited 

 of the relation of affinity, it may be perhaps best to adopt this, 

 without supposing additional possible modes, concerning which, 

 if they are admitted, many alternatives might be proposed. 4. The 

 vital properties producing the secretions combine with the secre- 

 tions, and exist in these fluids in the condition of informal life. 



