HISTORICAL DETAILS ON THE STRUCTURE OF THE KIDNEY. 107 



of the eighteenth. Our knowledge of the structure of the kid- 

 neys has rapidly progressed during the last thirty years, in 

 consequence of the application of the following methods of 

 investigation: 1. By. a comparison of the easily unravelled 

 structure of the organ in the lower Vertebrata (Bdellostoma 

 by J. Miiller, Coluber by Bowman). 2. By more precise and 

 definite methods of employing injections than had previously 

 been adopted, first by the application of atmospheric pressure 

 (Huschke) ; then by the use of more easily flowing material, 

 as the solution of carmine in gum employed by Gerlach, and 

 the mixture of glycerine and Prussian blue by Henle ; and 

 lastly, by very careful regulation of the amount and duration 

 of the pressure applied (C. Ludwig). 3. By the discovery of 

 means capable of effecting the solution of the connective 

 tissue and the bloodvessels while the urinary tubules are 

 left intact. Isaacs accomplished this by boiling fragments of 

 kidney in very diluted acids, as in sulphuric, phosphoric, 

 chromic, boracic, tartaric, and citric acids, and also by boiling 

 in chloroform (?). Henle introduced the use of cold concen- 

 trated hydrochloric acid for the same purpose, and Schweigger- 

 Seidel described the best mode of applying it. C. Ludwig 

 found the most advantageous proceeding to consist in boiling 

 small portions of the kidney in a mixture of hydrochloric acid 

 and alcohol, and then to macerate them for a day in distilled 

 water. 4. By a more accurate comparison of the structure of 

 the tubules in different parts of the same kidney (Henle). It 

 was thus that the discovery was made by Bowman and 

 Gerlach that the membranous investment of the glomeruli, 

 first described by J. Miiller, was the csecal extremity of the 

 tubuli, and became continuous through the neck with their 

 tortuous portion. Isaacs subsequently showed that the 

 tortuous portion of the urinary tubuli became attenuated 

 towards the limits of the cortex, and still more recently Henle 

 showed that the narrowed canal formed a loop in the medul- 

 lary substance; Henle also discovered at the same time that 

 the wide canals proceeding from the papilla underwent a 

 second division at the end of the medullary ray. The com- 

 munication between the branches of the collecting tubes and 

 the ascending limbs of the loops was then demonstrated by 



