110 Mr Carpenter on Unity of Function 



to investigate if this excretion like that of the liver is increased 

 when the functions of the lungs are impeded by disease. 



The exhalation of fluid is another part of the function of 

 excretion whicli might be separately considered in the same 

 manner ; but my limits forbid me to dwell upon it. I mvist 

 also be very brief with regard to the acknowledged organs of 

 secretion. We find that in plants the secretions are usually 

 formed to be stored up in the system, where they answer some 

 purposes not well understood ; a few are exuded from the sur- 

 face ; but it is not a little remarkable that some of the princi- 

 pal excretions of plants take place by the roots, the special or- 

 gans of an opposite function. I am disposed to believe that 

 this excretion, whose importance to the agriculturist is now ac- 

 knowledged, necessarily results from the process of exosmose 

 which must exist wherever endosmose is carried on ; and as it 

 would seem probable that a part of the descending sap, or of 

 the previously formed secretions, is mixed with the absorbed 

 fluid for the purpose of increasing its density and maintaining 

 the endosmose, it necessarily follows that some of it must be 

 lost in this manner. The greater activity of the vital functions 

 in animals, and the larger quantity of the solid ingesta, require 

 a more special provision for excretion besides that which takes 

 place by the resj^iratory and exhalant systems. Accordingly 

 we find biliary and urinary organs very low in the scale ; but 

 these are still formed upon the same general plan. We see the 

 simplest type of their structure in the mucous crypts of the 

 alimentary canal ; and as the excretory ducts are but prolonga- 

 tions of the external surface, so their minute ramifications by 

 which the gland is formed, are to be regarded in the same light. 

 As all the glands, therefore, have the same elementary struc- 

 ture, and differ only in the peculiar adaptation of each to sepa- 

 rate a particular constituent of the blood, it is a necessary re- 

 sult of the second law to which allusion has so frequently been 

 made, that either the general surface or either of the special 

 secreting organs shoidd be able to take on, in some degree, the 

 function of any gland whose duty is suspended ; and observa- 

 tion and experiment fully bear out this result. The " funda- 

 mental unity of the structure"" of glands has been made appa- 

 rent, not only by comparing those of different degrees of de- 



