254 



REN. 



scopical examination. In a part thus pre- 

 pared, I have sometimes seen the cilia in 

 rapid action throughout the whole length of 

 every tube in the field of the microscope, and 

 a more wonderful or beautiful sight can 

 scarcely be imagined. The motion commences 

 within the Malpighian capsule; the little par- 

 ticles floating in the liquid of the capsule are 

 darted into the orifice of the tube with mar- 

 vellous precision, and thence they are directed 

 onwards through the windings of the tube in 

 a current of liquid, which is propelled with 

 great regularity and speed. Much violence in 

 tearing up the specimen for examination ap- 

 pears to arrest the motion ; and when water is 

 added to the preparation, the epithelial particles 

 swell and fill up the cavity of the tube, and so 

 the motion is "retarded. When the cilia are 

 in slow motion, their form and the direction 

 of their movement may easily be seen ; but 

 when the motion has entirely ceased, I have 

 never been able to see them distinctly, even 

 with the best object glasses. The motionless 

 cilia appear to collapse and fall upon the 

 surface of the epithelium, and so become in- 

 visible. Since my attention was first directed 

 to the phenomenon in question, I have had 

 but little time to search for it in other ani- 

 mals ; but there appears reason to believe that 

 it exists in most of the higher animals, and pro- 

 bably even in man. The result of my own 

 observations may be thus briefly stated : In 

 the newt I have searched for ciliary motion in 

 the tubes many times, and have never failed to 

 find it in any kidney which I have examined. 

 I have searched for it in the frog twice 

 (f. e. in two individuals), and found the ciliary 

 motion very distinct in a considerable portion 

 of one tube. I have examined one snake, 

 and observed the motion very distinctly 

 throughout a large extent of several of the 

 tubes, as well as in the Malpighian capsules. 

 I have searched for the phenomenon in the 

 kidneys of some of the smaller Mammalia, as, 

 for instance, in the mouse and the rabbit, but 

 hitherto without success. I am not aware 

 that any other observations with reference to 

 this subject have been published, but possibly 

 there may be some with which I am not 

 acquainted. 



Epithelium of the pelvis and ureter. The 

 epithelium of the pelvis and ureter requires 

 only a brief mention ; it belongs to the lamel- 

 liform or scaly variety, and consists of flat- 

 tened, delicate, transparent scales, having an 

 angular outline caused by their lateral appo- 

 sition, and a nucleus which is generally ec- 

 centric. 



Function of the Malpighian bodies and urini- 

 ferous tubes. Before concluding this part of 

 our subject, it appears desirable to make some 

 allusion to the probable office of the several 

 parts of the kidney, whose structure has 

 passed under review. Mr. Bowman, in the 

 paper to which reference has so often been 

 made, has propounded a theory as to the 

 office of the Malpighian bodies which I 

 believe will soon be admitted as a true and 

 well-established doctrine, based as it is upon 



accurate observation, and confirmed by sound 

 reasoning and analogy. The theory in ques- 

 tion, and the facts and arguments in support 

 of it, are thus clearly stated by Mr. Bow- 

 man : 



" Reflecting on this remarkable structure 

 of the Malpighian bodies, and on their singular 

 connection with the tubes, I was led to specu 

 late on their use. It occurred to me that, as 

 the tubes and their plexus of capillaries were 

 probably, for reasons presently to be stated, 

 the parts concerned in the secretion of that 

 portion of the urine to which its characteristic 

 properties are due (the urea, lithic acid, &c.), 

 the Malpighian bodies might be an apparatus 

 destined to separate from the blood the watery 

 portion. This view, on further consideration, 

 appears so consonant with facts, and with 

 analogy, that I shall in a few words state the 

 reasons that have induced me to adopt it. I 

 am not unaware how obscure are the regions 

 of hypothesis in physiology, and shall be most 

 ready to renounce my opinion, if it be shown 

 to be inconsistent with truth. 



" In extent of surface, internal structure, 

 and the nature of its vascular network, the 

 membrane of the uriniferous tubes corresponds 

 with that forming the secreting surface of other 

 glands. Hence it seems certain that this 

 membrane is the part specially concerned in 

 eliminating from the blood the peculiar prin- 

 ciples found in the urine. To establish this 

 analogy, and the conclusion deduced from it, 

 a few words will suffice. 1. The extent of 

 surface obtained by the involutions of this 

 membrane will by most be regarded as itself 

 sufficient proof. But, 2. Its internal surface 

 is conclusive. Since epithelium has been 

 found by Purkinje and Henle in such enor- 

 mous quantities on the secreting surface of all 

 true glands, its use cannot be considered 

 doubtful. It never forms less than fths of 

 the thickness of the secreting membrane, and 

 in the liver it even seems to compose it en- 

 tirely, for there 1 have searched in vain for a 

 basement tissue, like that which supports the 

 epithelium in other glands. The epithelium, 

 thus chiefly forming the substance of secreting 

 membrane, differs in its general characters 

 from other forms of this structure. Its nu- 

 cleated particles are more bulky, and appear 

 from their refractive properties to contain 

 more substance, their internal tissue being 

 very finely mottled, when seen by transmitted 

 light. In these particulars the epithelium of 

 the kidney-tubes is eminently allied to the 

 best-marked examples of glandular epithelium. 

 3. The capillary network surrounding the 

 uriniferous tubes is the counterpart of that 

 investing the tubes of the testis, allowance 

 being made for the difference in the capacity 

 of these canals in the two glands. It corre- 

 sponds with that of all true glands in lying on 

 the deep surface of the secreting membrane, 

 and in its numerous vessels everywhere ana- 

 stomosing freely with one another. 



" These several points of identity may seem 

 too obvious to be dwelt upon, but I have 

 detailed them in order to show that in all 



