GLAND. 



491 



most complicated glands he relied solely on 

 his vascular injections, to the exclusion of the 

 evidence afforded by the much more satisfactory 

 researches of comparative and developmental 

 anatomy. If, as Professor Miiller has ob- 

 served, Ruysch had carefully examined his 

 injected organs with the microscope, he would 

 have found that between the most delicate 

 plexuses of the bloodvessels there is always 

 an additional substance destitute of vessels ; 

 although these organs, when seen by the naked 

 eye, appear to be stained in every direction 

 with the coloured injection.* But even ad- 

 mitting what frequently happens from a too 

 forcible injection, that the matter thrown into 

 the arteries is found in the ducts, this does 

 not prove that the small bloodvessels are con- 

 tinuous with the excretory canals ; for after 

 the sanguiferous vessels are filled, they easily 

 become ruptured, and so allow their contents 

 to escape into the ducts. It may further be 

 objected, that in all the glandular organs which 

 have been carefully inspected the commence- 

 ments of the excretory ducts are larger than 

 the least arteries ;f indeed, Ruysch's own 

 account of this imaginary continuity is very 

 vague, and the plates designed to illustrate 

 his theory, especially that of the kidney, are 

 any thing but satisfactory. As Ruysch did 

 not employ the microscope, it is impossible 

 he could have xeen that continuity which he 

 so confidently described; indeed, as Haller 

 remarks,! it i difficult, or rather as we should 

 say impossible, to demonstrate, with the aid 

 of the most powerful lens, the connexion of 

 the last arteries with the coats of the ducts. 



Not only did Ruysch adopt a most in- 

 sufficient mode in prosecuting his inquiries, 

 but he assumed as a fact what was in reality 

 a mere hypothesis, that secretion can only take 

 place from the open mouths or orifices of the 

 secerning arteries. The only point, therefore, 

 which he discussed was, whether the passage 

 of the arteries into the excretory ducts takes 

 place gradually and insensibly, or suddenly 

 and by the intervention of a follicle ; for it 

 never occurred to the anatomists of those times, 

 or even to Haller and his contemporaries, that 

 canals closed at their end by cul-de-sac, and 

 without open arterial mouths, could secrete. 



* Loc. cit. p. 8, $ 4. 



t Diameter of secreting canals. 



Line 



Parotid gland . . . 0-0099 (Weber). 

 Kidney .... 0-0166 (Meckel). 



Ditto 0-0180 (Weber). 



Testis .... 00564 (Miiller). 



Ditto 0-0648 (Lamb). 



Liver (in rabbits) . . 0-0140 (Muller). 

 Diameter of capillary bloodvessels. 



Line Line 



Parotid . . 0-0030 to 0-0039 (Weber). 



Kidney . . 0044 to 0069 (Muller). 

 Testis . . . 0-0030 to 0-0035 (Weber). 



Burdach Physiol. Fiinfter Band. p. 38. For 

 measurements in otber glands, see Muller De 

 Gland. Struct, p. 112 ; Valentin Handb. der En- 

 twickelungs-geschichte, p. 535 et seq. 



J El. P~hy. t. ii. p. 378. 



The existence of open mouths in the arteries 

 of the serous membranes, where they are generally 



But the true opinions of Malpighi did not 

 refer to the exact mode of termination pos- 

 sessed by the arteries; nor did he imagine 

 that any particular machine or follicle was 

 interposed between the arteries and the ducts : 

 his observations were rather directed to the 

 more important circumstances relative to the 

 disposition, formation, and extent of the true 

 secreting canals. 



In concluding these remarks on the hypo- 

 thesis of Malpighi, it is due to the character 

 of that illustrious cultivator of anatomical sci- 

 ence to state that his views are highly phi- 

 losophic, and in a general manner correct 

 that they are supported by numerous obser- 

 vations made on the glands of the lower ani- 

 mals, as well as on the development of the 

 liver during incubation and that he had thus 

 the sagacity to adopt the mode, which expe- 

 rience has shown is alone capable of resolving 

 this difficult question. 



It would be superfluous to enter into a de- 

 tailed account of the opinions advanced by 

 later anatomists, as they are for the most part 

 simply modifications of the hypothesis either 

 of Malpighi or of Ruysch. A few general 

 observations will therefore suffice. 



Ferrein has the merit of being the first wri- 

 ter who pointed out in a more distinct manner 

 than had been done by Malpighi, the great 

 importance of what are erroneously called the 

 excretory ducts, but which constitute, as we 

 have already shown, the true secerning struc- 

 ture. He remarks* that the cortical part of the 

 kidney is composed of a collection of white 

 cylindrical tubes, variously folded on them- 

 selves (canales corticales, or ducts of Ferrein,) 

 and he thought he had seen the same tubes in 

 the liver. The serpentine cortical canals have 

 been seen in birds by Galvani, to be filled with 

 cretaceous urine after the ligature of the ureter. 

 Although the researches of Ferrein are very 

 important, yet they want that support from 

 comparative anatomy, by which means alone 

 they could have been made subservient to esta- 

 blish any general principles. 



To Rolando belongs the honour of having 

 demonstrated the mode in which the glands 

 are developed from the alimentary canal. By 

 carefully conducted observations on the in- 

 cubated egg, he discovered that each of these 

 organs in the first instance consists of an ele- 

 vation or tubercle of the intestine, which sub- 

 sequently becomes hollowed and forms a canal 

 directly continuous with that of the intestine. 

 He also distinctly announced what has since 

 been demonstrated in all its details, that the 

 lungs are formed, like the glands, by a pushing 

 out of the upper end of the intestinal tube ; 

 and he further describes the mode in which 

 the bronchi and their subdivisions are deve- 

 loped. The error of those writers who contend 



called exhalants, has never been proved; on the 

 contrary, on examining, with a powerful micro- 

 scope, the circulation of the peritoneum in rabbits, 

 I have repeatedly observed that the small arteries, 

 after ramifying in a very complicated manner, 

 become distinctly continuous with the little veins. 

 * Mem. de 1'Acad. Roy. des Sc. 1749, p. 492. 



