April 14, 1892] 



NATURE 



565 



Schwann had shown that the muscular substance is in- 

 closed in a sheath of structureless membrane, which he 

 described as produced by coalescence of the cylindrical 

 cells from which it had originated. Bowman was the 

 first to observe that the " sarcous substance," as he called 

 it, i.e. the organized content of this tubular sheath, is 

 capable of being split, not only longitudinally into fibrils, 

 but also into disks, and founded on this observation a 

 new view of its structure — namely, that the sarcous sub- 

 stance consists oi cylindrical parts ("sarcous elements"), 

 each of which is a segment of a fibril. Bowman's obser- 

 vations were confirmed by KoUiker in the admirable 

 account of the structure of muscle given in the first 

 edition of the " Gewebelehre," published in 1 850. He, how- 

 ever, still regarded the existence of " sarcous elements " 

 as open to question. A few years later they acquired a 

 new title to recognition when Briicke, in his researches 

 on the structure of muscle with the aid of polarized light, 

 discovered that the sarcous substance, as observed by 

 this method, behaves as if it were made up of" a system of 

 cylindrical bodies, each having the properties of uniaxial 

 crystals with their axes parallel to that of the fasciculus." 

 Briicke did not pledge himself to the identity of these 

 cylindrical bodies (which he called " disdiaklasts ") with 

 Bowman's "elements," but rather regarded each such 

 element as a system of disdiaklasts. It would occupy 

 too much space to enter on this subject further. It must 

 suffice to say that the relation between the optical proper- 

 ties of sarcous substance and its microscopical characters 

 was soon fully recognized, and that Bowman's sarcous 

 elements still hold their own in every discussion on the 

 structure of muscle. 



(2) The Structure of the Mucous Metnbranes of the 

 Alimentary Tract. — On this subject Bowman's investiga- 

 tions were fundamental. If anyone were disposed to 

 doubt their claim to have been the starting-point of the 

 long series of researches by which our present knowledge 

 of the subject has been attained, he might at once satisfy 

 himself by comparing the clear account of the subject 

 contained in Bowman's article in the " Cyclopaedia of 

 Anatomy" (1843) with the vague statements which are to 

 be found in the best work on " General Anatomy " then in 

 existence, Henle's " AUgemeine Anatomie," published im- 

 mediately before. The contrast is striking. Within the 

 compass of a very few years Bowman had succeeded in 

 unravelling the structure of mucous membrane, and 

 arriving at new conceptions of the relations between its 

 constituent parts, which have survived to the present day, 

 notwithstanding the infinite amount of work which has 

 been done since, in the same field of inquiry — an achieve- 

 ment which appears the more worthy of admiration when 

 it is remembered that Bowman began as it were from 

 nothing, and had to rely on his own ingenuity for devising 

 his methods, and on his own dexterity for carrying them 

 out. For at that time and for many years after, the 

 methods of preparing tissues so as to display their 

 structure, which are now in everyone's hands, were 

 practically unknown. 



The Structure of the Kidneys. — The great discovery 

 which was announced in Bowman's paper on the structure 

 anduseof the Malpighianbodiesof thekidneys (Phil. Trans., 

 1842) was that of the connection between the Miillerian 

 capsule and the uriniferous tubes. The anatomists of the 

 time were unanimous in denying the existence of any such 

 communication, and Muiler himself — who, in his great 

 work on the intimate structure of the secreting glands, 

 published in 1830, gave the first account of the capsule — 

 characterized the suggestion that it might be connected 

 with the ends of the uriniferous tubes as a ^'■falsissima 

 opinio}'' In the edition of the " Handbuch der Physio- 

 logie," however, which immediately followed the appear- 

 ance of Bowman's paper, the great physiologist frankly 

 admitted his error. 

 The result next in importance of Bowman's research 

 NO. T 172. VOL. 45] 



was the explanation it enabled him to give of the renal 

 circulation. The knowledge which existed was extremely 

 defective. For, although it was known that there was a 

 communication between the capillaries of the glomeruli 

 and those of the convoluted tubes, the belief that the 

 capsules were closed sacs rendered it impossible to under- 

 stand their relation to the renal function. They were 

 indeed regarded merely as retia mirabilia, intended to 

 check the impetuous blood-stream in its course towards 

 the tubes. Miiller had, two years before the publication 

 of Bowman's paper, recognized that the renal tufts of 

 Myxine are contained in the urinary utriculi, but the 

 identity of these structures with the glomeruli of the 

 higher Vertebrates was overlooked by him until Bowman's 

 description served to explain his own observations on the 

 renal organs of the lower. 



The theory of the function of the kidney which sprang 

 out of Bowman's anatomical investigations was shortly as 

 follows : — The epithelium which lines the convoluted 

 tubes is the mechanism by which the characteristic con- 

 stituents of the urine are excreted. The water of the 

 urine is discharged by the Malpighian tufts by a process 

 partly physical, partly vital. These organs thereby serve 

 as an apparatus for the regulation of the water-content of 

 the blood, and thereby of the whole body. The grounds 

 for the theory were (i) the distribution of the capillary 

 blood-vessels on the external surface of the tubes ; (2) the 

 analogy of the renal epithelium with that of other secreting 

 glands ; (3) the absence of any such epithelium on 

 the surface of the tufts ; and (4) the consideration 

 that, by the arrangement of their capillaries, the 

 blood-stream through the tufts is retarded— a circum- 

 stance favourable to filtration. The theory was in so far 

 " vitalistic" that it assumed for the secreting epithelium 

 a special power or endowment, of which its structure 

 afforded no physical explanation. It was soon met by 

 another which regarded the whole process mechanically. 

 Only two years after Bowman's second paper, Ludwig's 

 article in Wagner's " Handworterbuch " appeared, in which 

 it was maintained that not only water but the salts and 

 other soluble constituents of the urine are discharged 

 by a process of filtration, and that the function of the 

 convoluted tubes of the cortex is not to secrete the 

 solids of the urine, but to reabsorb the water, and 

 thereby concentrate the product. Without entering 

 into details, it may be sufficient to say that the 

 theory of Ludwig was chiefly based on experimental 

 evidence relating to the immediate influence of purely 

 mechanical conditions in determining the rate of secre- 

 tion, which showed that the renal flow is instantly in- 

 creased by augmentation and diminished by decline of the 

 difference between the arterial and venous pressures, and 

 consequently varies with the rapidity of the renal blood- 

 stream. For twenty years this theory was tacitly accepted, 

 until in 1875 Heidenhain published the first of those 

 researches on the process of renal secretion which form 

 the basis of our present knowledge, and which resulted 

 in the reinstatement of the doctrine of Bowman that in 

 the kidney, as in other glands, secretion depends on the 

 active function of special secreting cells. The most 

 material difference between the doctrine now taught as 

 the outcome of the anatomical and experimental re- 

 searches of the last two decades, is connected with a 

 fact which remained unknown for many years after the 

 completion of Bowman's work — that the glomeruli or 

 Malpighian tufts are provided with epithelium, and that 

 their function is not, as Bowman thought, merely filtration. 

 The essential \)Qi\x\\.o{ agreeinentx's, that the living epithelial 

 cell contains in itself the essential mechanism for secre- 

 tion, and that it is on it that the influence of all external 

 conditions is primarily exercised. 



In the fifty years which have elapsed since Bowman 

 arrived at a true conception of the function of the kidneys, 

 an enormous and wholly unprecedented progress has been 



