166 THE AMERICAN MONTHLY [June, 



lined with very flat cells. There are some of them seen 

 in figure 4 which is a camera lucida drawing from na- 

 ture. The cells are but little wider than the nucleus ; 

 their side walls are inconspicuous or invisible; they are 

 in some cases even, contracted between the nuclei to less 

 than their diameter. In the convoluted portion of the 

 tubule the epithelium is very peculiar ; indeed, none 

 like it is to be seen in any other part of the body. The 

 cells of this part are shown in figure 5, in longitudinal 

 section ; and, in figure 6, in cross section. They have a 

 large nucleus and are densely filled with protoplasm. 

 Their basement membrane is very distinct ; the lumen 

 takes a zig-zag course owing to the different heights at- 

 tained by different cells. At the basal ends the cells 

 present a peculiar appearance, called " redded," from the 

 rod -like marks or striations that are found there. The 

 cells of this part of the organ are immediately succeeded 

 by the cells of the " malpighian corpuscle." 



This is one of the most curious structures in the 

 range of histology. In the actual section, it is only pos- 

 sible to see the structure in occasional and very favor- 

 able cases by the study of which a figure, No. 3, is con- 

 structed. It is seen to be a bulb with a double wall 

 such that the bulb has two cavities one which does not 

 open into the lumen of the tubule ; and a second, between 

 the two epithelial layers, which does open into the lumen. 

 This bulb is lined with small cubical cells. 



It is clear from this account of the kidney that the 

 epithelium is the active part of the organ and that its 

 function is some form of secretion. It is not so easy to 

 state clearly the difterent functions of the different parts 

 of the tubules which are implied by the difference in 

 the epithelium. Indeed this cannot be done with any 

 degree of confidence. How much mere filtration is an 

 important part of the process, or in how far true meta- 

 bolism is the mode of action, and whether the " malpig- 



