lo Nov., 1908.] Elements of Animal Physiology. 



67.5 



THE ELEMENTS OF ANIMAL PHYSIOLOGY. 



W . A. Osborne, M.B., D.Sc, Professor of Physiology and Histology, Dean 

 of the Faculty of Agriculture in the University of Melbourne. 



{Continued from page 640). 



XIV. Renal Excretion. 



The functions of the kidneys may be epitomised as follows : — 



1. Waste matter and foreign or harmful substances are removed from 

 the blood. 



2. The blood' is kept neutral in reaction. If it tends to get acid the 

 kidney removes the acid excess, if alkaline then the alkali excess is 

 eliminated. 



3. The blood is standardized as to the concentration and relative pro- 

 portions of its salts. As has been stated in the chapter on blood, not 

 only the total amount but the proportion between the individual salts in 

 the blood remains constant. As, however, the supplv of salts in the food 

 is verv variable, some adjustment is necessary and this we find in the 

 kidnev. 



THE MECHANISMS OF RENAL EXCRETION. 



The artery entering the kidney divides and subdivides until there are 

 formed thin, straight arterioles which radiate from within outwards. 

 Arising from these straight vessels and almost at right angles with them 

 are a number of smaller arterioles. These finer arterioles then form 

 peculiar structures just visible to the naked eye — the glomeruli. These 

 in reality are produced bv each fine arteriole being wound on itself to form 

 a convoluted tuft like a tangle in a cord. Wrapped closely around the 

 glomerulus is a double-walled capsule with an opening in it (Fig. 55). 



Fig. 5.5. Diagram showing straight arteriole, a ; glomeriUus, m ; capsule, /; 

 capillai-y plexus, »' ; and tortuous tube, t. (After Boirmaii.) 



A good picture of the shape of the glomerulus can be obtained by imagining 

 a piece of thin rubbej tubing folded into a knot or a bunch whilst around 

 this is closely applied a collapsed rubber balloon. Now the function of 

 the glomerulus is to act as a filter. The blood enters the glomerulus under 

 the pressure given it by the pumping heart and, as there is some resistance 

 to the outflow, it is forced not onlv through the capillary wall but also 

 into the adjacent wall of the capsule. A filtrate, therefore, collects in the 

 space between the two walls of the capsule. Now the membrane of which 



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