Ruysch* appears to have been the first to show that the urinary tubes may be injected through the arteries of the Malpighian bodies, and he supposed that the arteries become directly continuous with the urinary tubes. Boerhaave ± described the cortical portion of the kidney as being composed partly of glan dular Malpighian bodies, and partly of blood vessels, which form a plexus without being connected with the Malpighian bodies ; he also inferred the existence of two kinds of excretory ducts, the one kind being connected with the Malpighian bodies, while the others are directlycontinuous with the blood-vessels ; and he supposed that the more watery portion of the urine is excreted by the latter, while the denser portion prepared in the Malpighian bodies is carried off' by the first-mentioned ducts. Bertin agrees for the most part with Boerhaave as to the anatomy of the kidney, but he assigns to the Malpighian bodies the office of secreting the more liquid portion of the urine, and supposes that the denser parts are separated by those blood-vessels which, as he believed, are not connected with the Malpi ghian bodies, but are directly continuous with the urinary tubes.
Schumlansky§, while he confesses the great difficulty of arriving at an accurate knowledge of the structure of the Malpighian bodies and their connexion with the urinary tubes, ap pears to have had as definite an idea of these parts as it was possible to arrive at with the imperfect means of observation which he pos sessed. He describes the Malpighian bodies as consisting of a glomerulus of vessels, con nected on the one side with the arteries, and on the other with the veins, and invested by a cellular tissue in a manner which he does not very clearly explain. He believes that there is a close connexion between the Mal pighian bodies and the tubes, as manifested by the fact, that the tubes may be filled by a forcible injection of the Malpighian bodies through the arteries : further confirmation of this fact being afforded by the occasional pas sage of blood and other materials through the same channels, and the tubes being found filled with blood after death. With respect to the last observation, which he quotes from Bertin, he appears to have some doubt, and suggests that the vessels containing the blood may have been blood-vessels, and not urinife rous tubes.
Since the time of Schumlansky, whose work above quoted was published in the year 1788, scarcely any addition was made to our knowledge of the structure of the Malpighian bodies until the publication of Mr. Bowman's paper*, already so often referred to. In some respects, indeed, the description given of the Malpighian bodies by the best anatomists im mediately before the appearance of Mr. Bow man's paper, is less accurate than that of Schumlansky, and some of his predecessors. Thus, Miillert denied, i n the most positive man ner, the existence of any connexion between the Malpighian bodies and the tubes, and the possibility of injecting the latter from the former. Professor Miiller has since acknow ledged and confirmed the accuracy of Mr. Bowman's observations, which I shall now p.roceed to detail as much as possible in his
own words, because it would be impossible to depart much from the language of his paper without incurring a risk of losing something of the clearness which characterises the original.
The Malpighian bodies consist of a rounded mass of minute blood-vessels, invested by a cyst or capsule. The capsule was first par ticularly described by Miiller, who believed it to be closed on all sides except at one point, where it is perforated by the blood-vesscls. He accurately described the arterial branch as passing into the cavity of the capsule, where it gives off tortuous branches, which form arches, and then return to the point at which the artery enters, so that the tuft of vessels is free in the cavity of its investing capsule, being connected with the latter only at one point. Mr. Bowman, observing that the cap sule of the Malpighian bodies had an appear ance precisely similar to that of the basement membrane of the tubes, and seeing these similar tissues in such close proximity, was led to suspect that the capsule was in fact the basement membrane of the tubes expanded over the vessels, and after some time he suc ceeded in obtaining an unequivocal view of their continuity. This important result was arrived at after the use of the double injection. After the injection of some kidneys through the artery by this method, it was found that the injected material had in many instances burst through the tuft of Malpighian vessels, and being extravasated into the capsule, had passed off along the tube. (Figs. 153.3.156, 157.) Mr. Bowman afterwards made numerous injec tions of the human kidney, and of that of many of the lower animals, and in all, without excep tion, he met with the same disposition. He also examined thin slices of the recent organ with high powers of the microscope, and in this manner fully corroborated the evi dence furnished by injections. This mode of examination likewise led Mr. Bowman to the very interesting discovery of ciliary motion within the orifice of the tube and the con: tiguous portion of the Malpighian capsule. According to the observations of Mr. Bow man, the circulation through the kidney may be stated to be as follows : " All the blood of the renal artery (with the exception of a small quantity distributed to the capsule, sur rounding fat, and the coats of the larger vessels,) enters the capillary tufts of the Mal pighian bodies ; thence. it passes into the capillary plexus surrounding the uriniferous tubes, and it finally leaves the organ through the branches of the renal vein." (Fig. 152.) Following it in this course, I shall now give Mr. Bowman's description of the vascular apparatus, and the nature of its connexion with the tubes. I shall also refer to some observations which have been made since the publication of Mr. Bowman's paper, premising that Mr. Bowman's description is so singu larly accurate that it scarcely requires or admits of any, even the slightest, addition or modification, with reference to those par ticulars which it embraces.