SEC. 1. THE STRUCTURE OF THE KIDNEY. 



393. The kidney is a secreting gland constructed upon the 

 general plan of a compound secreting gland, but possessing special 

 features. The secreting portions, in which the divisions of the 

 main duct or ureter end, are not relatively short tubes with 

 branchings or lateral bulgings, that is to say, are not alveoli, but 

 are extremely long narrow tubules, with no branchings or lateral 

 bulgings. The whole body of the kidney is made up of these 

 constituent tubules, uriniferous tubules, tub-nil uriniferi, closely 

 packed together with just so much connective tissue as is suffi- 

 cient to carry a large supply of blood vessels, a certain number of 

 lymphatics, and nerves. 



Each uriniferous tubule, consisting of a single layer of epi- 

 thelium resting on a basement membrane which over the great 

 part of the length of the tubule is conspicuous and distinct, begins 

 in a peculiar structure called a Malpighian capsule, and for the 

 first part of its course pursues a path which is on the whole 

 very twisted and devious, during which it may, for the present, 

 be spoken of as a twisted tubule, corresponding to the tubulus 

 contortus of old writers. It subsequently takes a more straight 

 course, and is then called a straight tubule, tubulus rectus. At 

 its beginning and during its twisted course, the tubule lies, 

 for the most part, near the surface of the kidney, forming the main 

 part of the cortex of the kidney. During its straight course 

 it runs towards the deeper parts, converging towards the concave 

 border or hilus of the kidney, where the main duct or ureter 

 enters; the converging straight tubules forming together the 

 medulla of the kidney. While pursuing the first twisted and 

 devious part of their course, during the greater part of which 

 as we shall see they possess marked secretory characters, the 

 tubules do not join each other. During the latter straight part 

 of their course, when as we shall see their characters are those 

 of conducting rather than of secreting tubules, they repeatedly 

 join. After each junction the tubule, though wider than each 

 of the two tubules which joined to form it, occupies less 



F. ii. 43 



