FUNCTIONS OF THE LIVEE. 759 



more or less permanent tissue, and enter into the coherent framework 

 of the body; whereas, in the other, whilst a part thus remains to form 

 the gland-tissue itself, the essential products are discharged, in the 

 fluid state, by ducts, and are applied extrinsically to special functions 

 of the economy, sometimes, however, being then reabsorbed into the 

 blood. Both the nutritive and the secretive process yields various 

 results, according to the tissue in which they occur; nutrition forms 

 nerve, muscle, or bone, and secretion, saliva, pancreatic juice, or milk, 

 according to the nature of the tissue-elements which select, or deter- 

 mine, the separation of the nutrient or secreted materials from the 

 blood plasma. Both nutrition and secretion are modified by the quan- 

 tity and quality of the blood, and by the reactions of the vasi-motor 

 nerves. The nutritive and secretive processes may both be either con- 

 tinuous or intermittent, the former being illustrated by the continuous 

 formation of the epidermis and of mucus, and the latter by the inter- 

 mittent nutrition of the muscular and nervous tissues and the forma- 

 tion of the gastric juice. Lastly, the two processes resemble each 

 other, in being more active in some parts than in others, being more 

 so in the heart, the nervous centres, and the salivary glands and sweat 

 glands, than in the tendons, cartilages, bones, and the mucous and 

 sebaceous glands. 



SPECIAL SECRETIONS. 



Most of the secreting glands and their products have already been 

 considered, viz., the lachrymal glands and the tears, with the appen- 

 dages of the eyes ; the nasal glands, with the organ of smell ; the 

 ceruminous glands, with the ear; the sebaceous glands, with the skin; 

 and, lastly, the mucous glands of the mouth, fauces, pharynx, oesoph- 

 agus, stomach, and duodenum, the saliva and salivary glands, the gas- 

 tric and intestinal tubuli and their secretions, the liver and pancreas 

 and their respective products with the organs and function of Diges- 

 tion. The tracheal and bronchial mucous glands will be mentioned 

 hereafter, in the Section on Respiration. There remain, however, 

 certain general considerations concerning the liver and its offices, 

 which may be here noticed ; whilst the mammary glands with the 

 function of lactation, and the mucous, serous, and synovial secretions, 

 also require description. 



Secreting Function of the Liver. 



The source of the bile secreted by the hepatic cells is the exuded 

 plasma of the portal blood, which, .however, is joined by the blood 

 from the nutrient capillaries of the liver, derived from the hepatic 

 arteries. That the portal blood is essential, ajad the arterial blood 

 non-essential as such, to the formation of bile, is proved by the facts,* 

 that when the portal vein is compressed, the quantity of bile is dimin- 

 ished, and that when it is tied, bile is no longer secreted; whereas, if 

 the hepatic arteries be tied, its secretion is not necessarily arrested. 

 (Schiff.) In certain cases of malformation, the portal vein has been 



