210 MANUAL OF HISTOLOGY. 



membrane perfectly intact. A fresh kidney is necessary, and 

 one slightly infiltrated with fat makes the best specimens. 

 Another method is to embed the kidney of a dog or rabbit 

 in powdered chlorate of potassa, adding enough dilute nitric 

 or hydrochloric acid to cover the crystals. After some hours 

 the connective tissue in the gland will have been destroyed. 

 Portions of the medulla should then be placed upon a slide 

 with a drop of glycerine, and teased slightly. A great many 

 of the loops are broken in this way, to be sure, but still some 

 will be seen. By this method the epithelium of the narrow 

 branch is not destroyed. 



TJie epithelium of the looped tufiules. The descending 

 branch of the loop is small in diameter (0.02 mm.) and pos- 

 sesses a peculiar distinctive epithelium. The corpuscles are 

 flat, have prominent nuclei, and rest against the membrana 

 propria. The disproportionate size of the nuclei causes the 

 corpuscle to project into the lumen. But these prominences 



do not obstruct the passage, 

 for each one corresponds to 

 the space between two on 



Fro. 96. Kidney of dog. Descending portion of the Opposite side of the tU- 

 Henle'e looped tubule. r . 



bule, so that there is no bar 



to the urine, but the passage is made more or less spiral (Fig. 

 96). The corpuscles are of a light color. Specimens should 

 be made from a gland that has been macerated in a 5 per cent, 

 solution of the neutral chromate of ammonia; they should 

 be examined-in glycerine. The length of the narrow portion 

 of the loop is variable in man, the pig, and horse. 



The second portion of the looped tubule is wider and its 

 epithelium peculiar. In man both the loop and ascending 

 branch are wide, usually ; especially is this the case with loops 

 high up in the medulla ; in the rabbit it is the ascending 

 branch only that has this property. Generally speaking, the 

 length of the broader branch of the loop exceeds that of the 

 narrow portion. The diameter of the broad portion averages 

 0.04mm. The epithelium has the same character as that in 

 'the convoluted tubules ; it is striated and possesses rods. 1 It 

 is not precisely similar, however. The width of the individual 

 cells is not so great as in the former, and hence the lumen in 



1 Heidenhain : loc. cit. Henle : loc. cit. , p. 317. 



