164 Points in the Histology of the Hiiman Kidney. 



The necessary result of such work as this was in the first place 

 greatly to distend and enlarge the vessels, and in the next, to 

 encroach on all sides upon and to compress the cell tissue in which 

 they he imbedded. The double effect upon the examiner of objects so 

 prepared would naturally be on the one hand to magnify the im- 

 portance of the vessels, whilst on the other that of the cell tissue 

 would be diminished and even hidden altogether. 



Again, if we consider that the injecting fluid by which this 

 state of things was brought about was opaque, we shall get still 

 further insight into the process by which the tissue, now recognized 

 as composed of celLs, originally came to escape observation ; for in 

 addition to the circumstance of their great enlargement the vessels 

 in such a state of things could only be examined by reflected 

 light — a mode unfitted from its very nature to deal with the cell 

 tissue, as also because comparatively low powers only could be used 

 for the examination of specimens so prepared. 



It might a priori reasonably be thought that the introduction 

 and employment of transparent injections would efiectually correct 

 most of the faults in this category; but unfortunately perfect 

 injections of the capillaries of this kind, through the tendency to 

 transfusion of the fluid used for the purpose, are very difficult to 

 make ; and most of those seen display a blotted and confused out- 

 line, that I cannot doubt has served to confirm and perpetuate, 

 instead of discovering the faults in question. 



There are still many other sources of error in prosecuting 

 these inquiries, and not the least among them lies in the practice 

 of substituting the organs of the lower animals for those of the 

 higher. I wish carefully to avoid being understood as depreci- 

 ating in the least degree the value of comparative histology ; it is 

 the tendency only that I point to, existing in instances of difficult 

 research where it may be necessary to appeal to lower and simpler 

 organizations, to regard these latter not only as representing in a 

 general way more developed and comphcated structures, but actually 

 to look upon them as if they were almost, even if not quite, identical 

 with them. 



It is not necessary to extend this enumeration of possible and 

 probable sources of misinterpretation, further than to notice the 

 efiect of hardening processes upon the tissues of the kidney. 



To procure sections sufficiently thin for microscopic examination, 

 it is a very general practice to subject the organ to the action of 

 alcohol. It is certain, however, that after such treatment the kidney 

 in many important respects no longer presents its natural appear- 

 ance, and notably so with regard to the tubuh uriniferi ; for whereas, 

 as already stated, when examined in simple and indifferent media 

 they present no central canal, nor any the least trace whatever of 

 it, by exposure to the action of spirit they may often be made to 



