92 THE KIDNEYS, BY C. LUDWIG. 



obtains an investment that adheres closely to the vessels, and 

 of which we shall hereafter speak more at large. 



From the neck of the capsule to the commencement of the 

 ductus papillares, the wall of the tubuli uriniferi is composed 

 of a basement membrane (tunica propria), the inner surface of 

 which is lined by an epithelium. In general the basement 

 membrane appears to be homogeneous, and cannot be further 

 divided, but occasionally a nucleus can be brought into view 

 in its substance by carmine; and in some instances, and for 

 short distances, the same appearances occur in the tortuous 

 canals, when treated with nitrate of silver, as are presented by 

 the blood and lymph capillaries under the same conditions. 

 The basement membrane is as clear as glass, elastic, and readily 

 swells up in water. It can be very easily demonstrated in an 

 isolated condition. The epithelium lining the capsule forms a 

 single layer, and is nucleated. The shape of the nucleus is 

 usually the same in all instances; being spherical, sharply denned, 

 and with numerous granules scattered through its substance. 

 The cells, on the contrary, present various modifications. 



In the tortuous portions of the canals the nuclei, standing 

 at tolerably equal distances from each other, are imbedded in a 

 pulpy mass. The latter presents numerous fissures that are 

 particularly obvious in every tranverse section when a coloured 

 injection thrown into the urinary tubules has penetrated 

 them. These fissures, however, lie at very irregular distances, 

 and in brief it would appear that the mass investing the 

 nuclei, and to be regarded as cell-substance, is not differen- 

 tiated into separate cells. The epithelial pulp is only loosely 

 attached to the basement membrane; so that when fresh it 

 can be easily forced out of the isolated and divided tubules. 



How far the epithelial mass projects into the canal depends 

 upon the distension of the latter. If this, owing to an arti- 

 ficial arrest of the discharge of the urine, be considerable, the 

 epithelium lining the canal is flatter ; on the other hand, if 

 the kidneys have been empty before death, the epithelial ring 

 appears thicker. The pulpy investment consequently adheres 

 firmly to the basement membrane, and follows its alterations 

 of form. 



The material of which the pulpy bodies of the cells is com- 



