364 PRINCIPLES OF GENERAL PHYSIOLOGY 



some constituent of blood is necessary for the production of secretory activity by 

 stimulation of nerves. In the case of the pancreas, the combination of at least 

 three agents is necessary for secretion : oxygen (in greater amount than can be 

 dissolved in saline solutions), electrolytes, and secretin. Whether any other 

 constituent of blood, such as protein, is necessary is uncertain. It is obvious 

 that prolonged activity is only possible when materials for the formation of the 

 constituents are supplied. 



The electrical changes of gland cells when excited are of two kinds with 

 opposite sign. That associated with the secretion of water has an opposite 

 direction to that associated with the formation of the organic solids which 

 are characteristic of the secretion. 



The kidney requires special consideration. The glomerular filtrate, as it 

 passes along the tubules, undergoes three changes. Its total concentration is 

 increased by loss of water, on the one hand, and by secretion into it of waste 

 products, such as urea, etc., on the other hand. At the same time, it may lose, 

 by reabsorption, a large part of those solutes which are valuable to the organism, 

 such as sodium chloride, glucose, and amino-acids, but which are unavoidably 

 present in the filtrate. Foreign salts, such as iodides, appear to be excreted in 

 the tubules. 



Most diuretic substances act by diminishing the osmotic concentration of the 

 blood colloids ; some, by a specific action of some kind, perhaps by decreasing 

 absorption of water, etc., by the tubules. 



The formation of certain special secretory products is briefly discussed in the 

 text. These are acid and alkali, sepia, poisons, hirudin, silk, oxygen, luminous 

 substances, and electrical charges. 



LITERATURE 



General. 



Heidenhain (1880). Babkin (1914). 



Structure of Gland Cells. 

 Metzner (1907, 1). 



Osmotic Work Done. 



Von Rhorer (1905). 



Oxygen Consumption. 



Barcroft and Piper (1912). 



Salivary Glands. 



'Langley (1898). 



Secretion of Urine. 



Metzner (1907, 2). 



