ConqKiratice Physiology. 393 



system. Besides conveying to the various tissues the materials 

 required for their renovation, the current of circulating fluid 

 takes up, in animals especially, the particles which have dis- 

 charged their duty in the structure, and which are either to be 

 rendered again subservient to the process of nutrition, by ad- 

 mixture with alimentary matter newly absorbed, or to be sepa- 

 rated from the general mass, and carried out of the system. 

 This function is termed interstitial absorption, and is performed, 

 in the higher animals, by a special vascular apj)aratus. The 

 alimentary materials undergo various changes before becoming 

 part of the organised fabric, which are difficult to trace. The 

 first perceptible change is, the formation oi organisable products by 

 a new combination of the elements supplied by the food. This 

 aj)pears to commence, in vegetables, as soon as these elements 

 are absorbed ; and the same may probably be said of animals, 

 though the preparatory process of digestion seems to partake of 

 it. The organisation of these products aj^pears to commence in 

 the circulating fluid. The elaborated sap of plants, and the 

 chyle and blood of animals, contain these organisable products 

 in abundance (not merely mixed) ; and the existence of regular 

 globules in them results from incipient organisation, a charac- 

 teristic of nutritious fluids. From these materials the indi- 

 vidual tissues of the fabric are created and renewed by the 

 process of nutrition (or assimilation^; each deriving from the 

 blood that portion which its composition requires. To preserve 

 the circulating fluid in the state required for performing its func- 

 tions, means are provided for elaborating certain fluids having a 

 destined use in the economy, and for se23arating and carrying 

 out whatever may be superfluous. These are termed secretion 

 generally, the latter excretion. In proportion to the complexity 

 of the structure, we find the excreting organs multiplied, and 

 their products varied, this function being no less important 

 than absorption. The loss of fluid by exhalation, and of super- 

 fluous carbon by expiration (a kind of excretion), is constant 

 in all living beings." 



-The views above stated of Dr. Carpenter on reproduction, or 

 generation, difler from those of other physiologists. It has been 

 customary to state that it is produced by excess in the nutritive 

 system. Liebig, on the same subject in animals, takes this 

 view, and notices the power of accumulating nutritious matter, 

 at certain periods, as proofs of this. The accumulation, how- 

 ever, may be the effect and not the cause, a provision, not 

 an inducement ; the case of insects, which are destitute of this 

 power while the nutritive functions are most active, would 

 seem to infer as much. It is perhaps, however, not so certain 

 that a comparative cessation of the one should take place before 

 the other commences. Over-fed plethoric beings cannot be said 



