THE KIDNEYS. SECRETION OF URINE. 



595 



cerned in the introduction of aliment into the system. The following are the 

 points in the minute structure of these organs which are of most importance in 

 their Physiological relations. 1 The distinction between the cortical and medul- 

 lary parts of the Kidney essentially consists in this that the former is by far 

 the most vascular, and the plexus formed by the tubuli uriniferi seems to come 

 into the closest relation with that of the sanguiferous capillaries, so that it is 

 probably the seat of the greater part of the process of secretion ; whilst the 

 latter is principally composed of tubes, passing in a straight line from the for- 

 mer towards their point of entrance into the ureter. The adjoining figure (Fig. 

 163) represents the appearance presented by a portion of an injected Kidney, as 

 seen by the naked eye, and under a low magnifying power. The tubuli urini- 

 feri, in passing outwards from the calices, increase in number by divarication 

 to a considerable extent, as shown in Fig. 165, but their diameter remains the 

 same. When they arrive in the cortical substance, their previously straight 

 direction is departed from, and they become much convoluted. The closeness 

 of the texture formed by their interlacement with the bloodvessels renders it 



Fig. 164. 



Portion of the Kidney of a new-born infant : A, 

 natural size ; a, a, Corpora Malpighiana, as dispersed 

 points in the cortical substance; b, papilla. B, a 

 smaller part magnified ; a, a, Corpora Malpighiana ; 

 b, tubuli uriniferi. 



Portion of one of the tubuli uriniferi, from the 

 kidney of an adult ; showing its tesselated epithe- 

 lium. 



difficult to obtain a clear view of their mode of termination; but they seem to 

 inosculate with each other, so as to form a plexus, with free extremities here 

 and there (Fig. 165); the number of these free extremities, however, does not 

 appear to be nearly equal to that of the uriniferous tubes themselves. 3 The 

 tubuli are lined with an epithelium, the cells of which are irregularly roundish 

 or polyhedral in form (Fig. 164); each cell contains a nucleus; and in its inte- 



1 See especially Mr. Bowman's Memoir in the "Philosophical Transactions," 1842; 

 also Goodsir in "Edinb. Monthly Journal," 1842 ; Gerlach, Bidder, and Kolliker, in " Miil- 

 ler's Archiv.," 1845; Toynbeein "Med.-Chir. Trans.," 1846; Johnson in " Cyclop, of Anat. 

 and Phys.," art. "Ren.;" Gairdner in "Edinb. Monthly Journal," 1848; and Frerichs, 

 "Die Bright' sche Nierenkrankheit und deren Behandlung," 1851. 



2 In Mr. Bowman's opinion, all the free extremities of the tubuli uriniferi include Cor- 

 pora Malpighiana ; and the appearance of csecal terminations, such as those represented 

 at 1 and 3, Fig. 165, he regards as an optical illusion, caused by a change in the direction 

 of the tubuli. which occasions them to dip away suddenly from the observer. 



