REN. 



241 



empty, they cannot be distinguished from the 

 fibrous tissue in which they are imbedded ; it 



Fig. 151. 



Section of the kidney, showing the relation of the 

 tubes and blood-vessels to the fibrous matrix, a, 

 portion of a tube ; ft, section of a blood-vessel ; e, 

 fibrous matrix. Magnified 100 diameters: from a 

 specimen prepared by Mr. Bowman. 



is only by the contrast of their colour when 

 filled with blood, or with injection, that it can 

 be ascertained that, in addition to the capil- 

 lary vessels which surround the tubes, there 

 is a connecting fibrous tissue, the office of 

 which appears to be to support and retain in 

 position the various complicated parts 

 tubes, Malpighian bodies, and blood-vessels 

 amongst which it is placed.* 



Tubuli Uriniferi. The tubuli uriniferi are 

 so intimately connected with the Malpighian 

 bodies, that it is not possible to give a com- 

 plete description of one of these structures 

 without an occasional reference to the other. 



The general course and mode of division 

 of the tubes, as well as their connexion with 

 the Malpighian bodies, is best ascertained by 

 the examination of specimens in which the 



* Mr. Toynbee, in a paper " On the Minute 

 Structure of the Human Kidney," i alludes to the 

 presence of " parenchymal cells " in the kidney, to 

 which he assigns an important function in preparing 

 the blood for further changes in the tubuli, in 

 which he says " cells of a character not very dissi- 

 milar are seen." He considers that "the relation 

 in which the parenchymal cells stand to the ner- 

 vous system is a subject of great interest ;" and he 

 arrives at the conclusion that the nervous filaments 

 " end by becoming continuous with the parenchyma 

 of the organ precisely as he has observed those in 

 the tail of the tadpole to become directly continuous 

 with the radiating fibres of stellated corpuscles, and 

 the filaments from the corpuscles to communicate 

 with each other." He further states that in certain 

 diseased states of the kidney, " the parenchymatous 

 cells will be found not merely increased in size, but 

 adipose depositions will be visible throughout them." 

 The account which Mr. Toynbee gives of these so- 

 called parenchymal cells is not such as will enable 

 me to state with confidence to what particular ap- 

 pearances his description of them applies ; but as I 

 have never been able to satisfy myself of the exist- 

 ence of any such cells as those referred to by him, 

 and as I am not aware that they have been recog- 

 nized by those anatomists who have most carefully 

 studied the structure of the kidney, I cannot con- 

 firm Mr. Toynbee's observations as to their func- 

 tion, their connexion with the nerves, or the patho- 

 logical changes which they undergo. 



1 Med. Chir. Trans., vol. xxix. 



VOL. IV. 



tubes have been filled by injection ; but our 

 knowledge of the essential structure of the 

 tubes, and particularly of their epithelial lining, 

 would be very incomplete without a careful 

 examination of uninjected specimens with a 

 high magnifying power. 



Mode of injecting the Tubes. The tubes 

 may be more or less completely injected in 

 two modes : 1st, by a liquid thrown into 

 them from the pelvis of the kidney ; and 2dly, 

 by the extravasation of materials forcibly in- 

 jected into the blood-vessels of the Malpighian 

 bodies. By the first mode the injected ma- 

 terials are made to enter the open mouths of 

 the tubes at one extremity, and to pass 

 towards the other, which, as will presently be 

 shown, is a closed extremity ; while by the 

 second method the injection is admitted into 

 the closed extremities of the tubes, whence it 

 flows towards their open mouths, and so in 

 some instances escapes into the pelvis of the 

 kidney. By the last mode the tubes are often 

 completely filled from one extremity to the 

 other, while by the first method of injection 

 they are generally very imperfectly filled, and 

 this even when the air-pump has been used to 

 aid the flow of the injection into the tubes. 

 A consideration of the structure and relation of 

 the tubes will show that this result is a neces- 

 sary consequence of the anatomical dispo- 

 sition of the parts. Mr. Bowman remarks *, 

 " To those who are acquainted with the 

 practical difficulties of the injection of the 

 ducts of glands in general, and especially of 

 those which are very tortuous, the following 

 considerations on this subject will probably 

 appear conclusive. Even of the testis (where 

 the tubes are far thicker and stronger in their 

 coats, and much more capacious than in the 

 kidney), there are not ten specimens that can 

 be pronounced at all full in the museums of 

 Europe : and there is no evidence that, even 

 in the best of these, the injected material has 

 reached the very extremities of the tubes. 

 In the kidney, the tubes are exceedingly tor- 

 tuous after leaving the Malpighian bodies, and 

 only become straight, in most animals, in pro- 

 ceeding towards the excretory channel to 

 discharge themselves. The way towards their 

 orifices is so free in a natural state, that their 

 fluid contents exert no distending force upon 

 their walls. Accordingly their walls are ex- 

 ceedingly feeble ; the basement membrane on 

 which their strength mainly depends is very 

 delicate, and easily torn. They are therefore 

 incapable of offering much resistance to a fluid 

 impelled into them from the pelvis, but burst 

 easily if it be forcibly urged. But were the 

 coats ten times as tough as they really are, 

 injection could not penetrate far into their 

 convoluted portion, unless pushed with much 

 force ; and this for two reasons : 1st, the fluid 

 which the tubes already contain has no means 

 of escape before the injection, since these 

 canals end by blind extremities in the Mal- 

 pighian bodies ; 2dly, the layer of epithelium is, 

 immediately after death, very prone to separate 



* Philosophical Transactions, 1842. 



R 



