QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 199 



organized structures. A considerable portion of the proto- 

 plasm of the cell has underj^one important modifications, 

 being converted into a large number of very delicate cylin- 

 drical bodies, which Heidenhain calls rods (stabchen). 

 Attached by their outer ends to the tunica propria, they 

 traverse the epithelial layer in a radial direction, being im- 

 bedded in a very small quantity of amorphous interstitial 

 substance. The nuclei, which lie at regular intervals, sur- 

 rounded by a more or less considerable quantity of undifferen- 

 tiated protoplasm, are enveloped by these rods, and what have 

 been till now described as dark granules in the body of the 

 cells are for the most part nothing but cross sections of the 

 rods. This conclusion is arrived at from investigations chiefly 

 on the dog's kidney, but the author recommends (for the 

 study of the organ in a perfectly fresh state) those of the rat 

 and the hedgehog. The perfectly fresh specimens, examined 

 either in longitudinal or transverse section (with objective 8 

 or 9 of Hartnack), show a striated appearance, indicating the 

 presence of the rods. The latter are seen more clearly in 

 sections from specimens hardened in neutral chromate of am- 

 monia (5 per cent.) and alcohol successively. Another method 

 of hardening is to inject a saturated solution of potassium 

 chloride into the renal artery, and then harden in spirit. 

 Isolation of the elements is best effected by maceration in 

 caustic soda (33 per cent.), or in the 5 per cent, solution of 

 neutral chromate of ammonia. The rods thus isolated are 

 found to be cylindrical structures, somewhat variable in size, 

 some being as long as the whole thickness of the epithelial 

 layer, others shorter, and varying also in breadth. The 

 nuclei of the epithelium are also isolated by the same means, 

 and found to be surrounded by a protoplasmic mass, which 

 in some animals is separated from the rods, in others con- 

 tinuous with them. There is also a small quantity of residual 

 cement substance betAveen the rods. The nuclei and their 

 surrounding cell body never touch the wall of the tube, which 

 only shows the attachment of the rods. In the looped tubes 

 of Henle substantially the same relations are seen, but no rods 

 were discernible in the epithelium from the straight tubes of 

 the pyramids or the large collective tubes of the papillae. 



The comparative structure of the kidneys of birds and 

 snakes is illustrated by observations which we must pass 

 over. c . 



Experiments on the function of the kidneys were made by 

 Chronsczewski's method of injecting indigo sulphate oi soda 

 into tlie circulation (pure and specially prepared solution is 

 necessary, that usually obtained being impure). Heidenhain 



