CHAP.XXX1I.] RECREMENTITIOUS SECRETIONS. 449 



5. Certain portions of the bile, already considered (see p. 258, vol. ii. ), 

 by the liver. To these may be added sundry constituents of the 

 faeces, of imperfectly known composition, but supposed by Liebig 

 to be imperfectly oxidized matter,* escaping by the mucous lining 

 of the intestinal tract, probably by the tubes of Lieberkiihn and 

 by the solitary glands ; and lastly, also, whatever substances are 

 taken in as food and absorbed into the blood, but which fail to be 

 assimilated, either from their being superfluous in quantity, or in- 

 capable of serving any purpose in the ceconomy. 



Secretions which are not composed of excrementitious Substances, 

 and ivhich serve important Offices in the (Economy. Other secre- 

 tions f and this is a large and diversified class) do not consist of 

 waste materials, the results of the disintegration of the tissues, but 

 are thrown off in certain situations where they are to perform a 

 part useful or necessary to the protection or preservation of other 

 organs, or of the whole body, or of the species. Of these, speaking 

 generally, it may be said that they are formed, as well as elimi- 

 nated, by the several organs which furnish them ; that they retain 

 more or less resemblance, in chemical constitution, to the food 

 and the nutritious parts of the blood ; and that, in many respects, 

 they are allied to the living tissues of the body from which they 

 are separated. 



The highest example which can be given of these qualities is that 

 of the male and female elements, the semen and the ova, which go 

 to form the new being, and which are the production of organs 

 essentially secreting. Here the secreted matter retains its organ- 

 ized form and its living properties, which latter are of so elevated 

 a character, as to end in the development of an entire organism 

 like that which has furnished the secretion. 



Other examples, in which these qualities meet less decidedly, are 

 presented by the milk, and by some of those secretions which have 

 been already considered under the head of the digestive function, 

 such as the saliva, the gastric juice, and the pancreatic fluid. 

 These are poured out to mingle with the food, and variously to 

 facilitate its entry into the blood ; and there can be no doubt, that 

 after having duly effected this object, they become in a consider- 



* The fseces have lately been subjected to chemical investigation by Dr. 

 W. Marcet, who has discovered an organic crystalline substance of an alkaline 

 reaction, to which he gives the name of Excretine, an acid olive-coloured sub- 

 stance, of a fatty nature, Excretolic acid, and a fatty acid, having the proper- 

 ties of Margaric acid, but not constantly present. "Proceedings of the Royal 

 Society," vol. vii. No. 6. 



