SECRETION. 267 



Though many constituents of secretions are not discoverable 

 in the blood, some curious circumstances are related to show the 

 importance of the qualities of the blood, as well as of the secretory 

 organs, in producing peculiar substances. It is asserted that the 

 blood will contain bile if secretion in the liver is prevented by 

 tying the vena portae ; and urea appears in the blood, if the kidneys 

 are removed, so that none can be secreted., 



In secretion the change must be chemical. Gelatine is merely 

 decarbonised albumen; diabetic sugar is urea deprived of azote 

 and some of its hydrogen ; and the labours of Dr. Prout are dis- 

 playing the various proximate principles of animals and vegetables 

 to have the same elements, and to differ merely in the proportion 

 of component water, or by the presence of a minute proportion of 

 additional substance hitherto regarded as accidentally present 

 and unimportant. Some substances, it is true, exist in vegetables 

 and animals that cannot at present be entirely ascribed to exter- 

 nal sources. Dr. Prout, from most careful experiments, concluded 

 that there is strong reason to believe that the bones of the chick 

 are not derived from the shell, but from internal production.? 

 Vauquelin found the lime of the excrements of hens, and of the 

 shell, to be too great to be ascribed to the food<i; and the products 

 of plants, fixed in sand and moistened with distilled water, contain 

 so much more carbon and earthy matter than can be supposed to 

 enter them from the atmosphere or the water, that Dr. Bostock 

 and others of our best chemists conceive their existence inex- 

 plicable entirely upon these sources. r If such is the fact, we 

 may conclude that these substances, though classed, as air and 

 water once were, as elements, because not yet decomposed by 

 chemists, are really not so ; for creation by natural powers is 

 impossible. 8 But, although secretion is, I apprehend, merely a 

 chemical process, dependent upon the quality of the blood, 



Prevost and Dumas found that the removal of one kidney has no particular 

 effect ; but that the removal of both occasions copious vomiting and purging of 

 brown liquid, and death j and 5 oz. of blood yielded 9 i. of urea. Annales de 

 Chimie, torn. xxii. 



P Phil. Trans. 1822. 



1 Annales de Chimie) torn. xxix. 



r See Dr, Bostock, 1. c. vol. ii. p. 387. sq. Braconnot concludes that earths, 

 alkalies, metals, sulphur, phosphorus, carbon, and perhaps azote, are thus pro- 

 duced. The immense quantities of calcareous strata, which appear to be the 

 remains of marine animals, are thought referable to organic production only. 



Dr. John ascertained that some plants convert potass into soda, Professor 

 Lindley, 1. c. 



