464 URO-GENITAL SYSTEM. 



In a general way, then, it may be said that the Hood of the 

 capillaries in the glomerulus is subjected to quite a consider- 

 able pressure, and that in the interstitial or parenchymatous 

 capillaries there exists a pressure less than that of the blood 

 in the ordinary capillaries. 



The intensity of the pressure in the first system has 

 attracted the attention of every physiologist, and all admit 

 that in this system there should occur a mechanical filtration 

 which would be the first phase of the source of the urinary 

 secretion, but there is a want of agreement with regard to 

 the character of the liquid filtered. Some (Bowman) con- 

 sider that it is simply water; others (Ludwig) that it is 

 urine, but largely diluted, which by the loss of a portion of 

 its water will become the urine that is afterwards poured 

 into the bladder. 1 



If we apply here the information that physiology of the 

 capillaries of other portions of the body has supplied, and 

 recollect that the capillaries of the glomerulus present a 

 structure similar to those of every other region ; we ought to 

 conclude that in these capillaries there is normally produced, 

 in view of the normal and permanent excess of the pressure, 

 what is abnormally produced in every other region when the 

 blood pressure is exaggerated. Following out this sugges- 

 tion, when a ligature compresses the veins of the forearm, 

 when from a pathological cause the abdominal venous circu- 

 lation is arrested ; in brief, at any time that the pressure in 

 the capillaries is increased, these latter will allow the liquid 

 portion of the blood to filter out through their walls, with all 

 the constituent elements of the serum, viz., water, albumen, 

 etc. The supposition is, then, authorized that the same phe- 

 nomenon will occur in the glomerulus, and that this latter 

 does not allow pure water, but the serum of the blood with- 

 out making any distinction between its elements, to pass into 

 the uriniferous tube. 



This view is fully confirmed by an experiment already per- 

 formed in nature by pathology : when an uriniferous tube, in 

 any part of its course, becomes obliterated, its initial portion 

 continues to receive the products of filtration in the glomer- 

 ulus which have accumulated in the obliterated portion ; this 

 latter enlarges, and finally forms a cyst of variable size. 

 Now if the contents of similar cysts be analyzed, these are 



1 See Cl. Bernard, " Lecons sur les Liquides de 1' Organisme. " 

 Vol. II. Legon 0. 



