116 GLANDS. 



floating in the water, under the microscope, it could be rolled over 

 and over, so as to show various points of the surface of the tuft, 

 covered by nucleated cells" 



" By the different processes first mentioned," he concludes, " I 

 consider the existence of nucleated cells upon the surface of the 

 Malpighian tuft, and, consequently, its analogy with the other 

 secreting organs, as conclusively demonstrated." These descriptions 

 are illustrated by several highly satisfactory drawings, pp. 404-407. 

 The modesty of the author prevented him from emphasising the ori- 

 ginality of the observation contained in the lines in italics, which were 

 introduced by the writer. The importance of the anatomical fact, 

 thus clearly demonstrated, that the Malpighian bodies of the kid- 

 ney are covered by an epithelium, the cells of which are distinctly 

 different from the ordinary epithelium of the urinary tubes, can be 

 estimated by a reference to the fact that the ingenious and almost 

 universally received theory of the action of the kidney, announced 

 in 1842 by Mr. Bowman, in his paper in the Philosophical Transac- 

 tions, is founded mainly on the belief that the surface of the vessels 

 composing the Malpighian tuft were naked and bare. In a subse- 

 quent paper " on the function of the Malpighian bodies of the kid- 

 ney" read before the N. Y. Academy of Med., February 4th, 1857, 

 its ingenious author, by a series of novel and interesting experiments, 

 demonstrates, satisfactorily, that the function of the Malpighian tufts 

 of the kidney is not the mere separation of water from the blood, as 

 Bowman asserts, and that, on the contrary, it separates from the 

 blood most of the proximate elements of the urine, any element of the 

 urine which is not secreted by the Malpighian tuft, being, probably, 

 afterwards separated by the epithelial lining of the tubes. Trans. 

 N. Y. Academy of Med., Vol. I., Part IX., p. 452. 



Another anatomical point settled by Isaacs is, that the ultimate 

 ramifications of the renal artery do not all terminate in Malpighian 

 tufts, although the great majority of them do so. At p. 385, he 

 gives a wood-cut representing a small branch of the renal artery, as 

 seen under the microscope, " which divides into two twigs, one of 

 which supports at its extremity the Malpighian coil or tuft of capil- 

 laries, whilst the other enters into the venous plexus." 



He also confirms, conclusively, the opinion of Bowman as to the 

 relation existing between the Malpighian tufts and the expanded 



