BIOLOGY IN HUMAN AFFAIRS 



membrane — in other words, a process explicable by known 

 laws of physics and chemistry. On the other hand, some 

 have maintained that glomerular function cannot be ex- 

 plained as a filtration, cannot be expressed at present in 

 terms of physical or chemical laws, or duplicated outside 

 the body. Since the living cells around the glomerulus 

 are, on this view, supposed to furnish the energy for fluid 

 elaboration, the glomerulus is said to "secrete" fluid. 

 Now, how has evidence been obtained favoring one or 

 the other of these theories of glomerular function? We can 

 only review here briefly some of the more important 

 results of recent research, which seem at present to "prove" 

 the filtration theory. The structure of the glomerulus 

 makes it ideally adapted to function as a filter, and this 

 argument from structure has been frequently used. As the 

 rate at which filtration will take place across a membrane 

 will depend, other things being equal, on the pressure- 

 head available, the relation of urine formation to blood 

 pressure has been studied. Two careful series of recent 

 experiments have shown that the rate of urine formation 

 by the kidney — the rate of fluid excretion — varies directly 

 with the blood pressure. Again, if glomerular function 

 is filtration, the fluid formed at the glomerulus should 

 contain all the constituents of the blood plasma in the 

 same concentrations as they exist in blood, except the 

 plasma proteins to w^hich the filter is impermeable. Quite 

 recently a group of workers in Philadelphia have succeeded 

 in collecting fluid from the frog's kidney immediately 

 after it has passed through the glomerulus — a structure in 

 this animal less than one hundredth of an inch in size. 

 The fraction of a drop of fluid obtained has been subjected 

 to analysis, and found to contain certain constituents in 

 the same concentration as they are present in blood plasma, 

 a finding strongly supporting the filtration theory of 

 glomerular function. 



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