In the lower animals, or at least in many of them, the lymphatics seem to be more nume rous. Moreschi distended the lymphatics of the spleen in fishes (in whom they possess no valves) from the trunk, and he says that the in jected spleen appeared to consist almost solely of a network of absorbents. But in another place he freely states that the spleen consists, so to speak, of nothing but vessels. In a Testudo mydas, Tiedemann and Gmelin saw all the absorbents of the small intestine going to the spleen, in which, by interlacing with arteries and veins, they formed a network. From this network large branches, like the emer gent vessels of the lymphatic glands, took their course towards the thoracic duct. Al most all the older writers recogniscd the rich ness of the spleen in lymphatics, which later examiners have but confirmed. But it will be well to set forth one fact which, in my opinion, is not sufficiently estimated, namely that even here absorbents are only sparingly present in the interior of the spleen ; at least I have found this to be the case in the pig, ox, sheep, &c. Here the superficial lymphatics are, as is well known, very numerous, and this fact seems to me to correspond with the circumstance that in these animals the serous and fibrous coats are only loosely connected to each other, and contain many vessels in the loose areolar tissue between them. But, on the other hand, if the vessels in the hilus be exatnined, only a few scattered trunks can be seen, a condition which stands in extraordinary contrast with the very nu merous lymphatics of the coats. Thus, for instance, in the hilus of a large calf I found only four trunks of lymphatics, which toge ther possessed a diameter of only 176-1000ths of a line ; while the interior of the spleen is also poor in lymphatics, for, so far as I have seen, the numerous plexuses of lymphatic trunks in the coats of the spleen have no rela tion with the interior of the organ, but at least the greater number of them belong solely to the subserous areolar tissue.
As to the distribution of the lymphatics in the spleen, it may easily be seen, by observ ations on oxen, that they only follow the course of the arteries, lying with these in side the sheaths; while the veins, which take a solitary course, and (as was before mentioned) possess no sheath, are also devoid of these companions. I have not seen the comtnencement of the lymphatics, yet I can state for a certainty, that they. have nothing to do with the Malpighian corpuscles, since these corpuscles are completely closed, as was before mentioned. And, I will add, in support of this my view, that the small arte ries which pass to the Malpighian corpuscles are no longer accompanied by lymphatic vessels ; at least microscopic examination detects no trace of such vessels within their sheaths. Just as little does the pulp possess any lymphatics ; for if these, like the nerves (see below), pass from the sheaths of the arteries into the pulp, they would in such a case be visible. And from what has been said, I conclude that the lymphatic vessels of the interior of the spleen belong wholly and solely to the sheaths of the arteries, and not in the least to the pulp or the Malpighian corpuscles ; and thus that here they play pre cisely the same rather subordinate part which they do in the liver, where they pertain to the capsule of Glisson, and not to the glandu lar substance ; or as in the kidneys, in the interior of which they only accompany the bloodvessels. Concerning the structure of the lymphatic vessels, I can only state thus much ; that in the calf they possess, at least in their main trunks, three membranes :— 1. An epithelium similar to that of the arte ries ; 2. A circular fibrous membrane, com posed of two or three layers of very distinct unstriped muscular fibres ; 3. An outer mem brane of white fibrous tissue. Valves occur in the deep as well as in the superficial lymph atics.
8. Nerves.— The nerves of the spleen arise from the splenic plexus, and accompany the splenic artery as two or three interlacing trunks, and divide in such wise at the giving off of its branches, that each artery receives one, or very frequently two nerves, which accompany it, and here and there anastomose with each other. The thickness of the primary nervous trunks varies very much in different creatures. Thus in the sheep, and especially in the ox, they are of really a colossal size, and taken all together, their diameter equals that of the empty and contracted splenic arteries; while in man and the pig they are no way remarkable in size, and are many times smaller than the arteries. These differences, which led the earlier authors to speak of the splenic nerves in similarly different expressions, were at first altogether inexplicable to me, since I could not understand why the spleen of one animal should possess so much larger nerves than another. On a more careful examin
ation, the microscope gave a very simple and unforeseen explanation. The uncommon size of the splenic nerves of Ruminantia depends solely on this,— that the white fibrous tissue of these nerves is disproportionally developed in the shape of the so-called " fibres of Remak," while it is much less prominent in the same nerves of other animals. A com parison of the splenic nerves of the pig and calf has taught me that if we limit our inquiry to the number of primitive nerve fibres, scarce any difference exists between the two sets of nerves. But, on the other hand, the primi tive nerve fibres of the pig lie very closely together, so that they cannot be numbered without considerable trouble while as an exarnple of their condition in ;he calf, I will adduce the following : — The trunks of the nervesentering the hilus were seven in number, with a diameter of -.57, -2, -048, -6, -48, -48, -6 (line); and they contained respectively only 28, 7, 6, 9, 13, 9, 22 primitive nerve fibres. In the lower animals, the nerves may be followed with the knife for a considerable distance into the spleen, much further than in man ; and with the help of the microscope, I have very frequently followed them even on the arteries which go to the Malpighian corpuscles. I have been just as little able as Remak to find any ganglia on the arteries in the interior of the spleen. Concerning their mode of termi nation, I am only able to say thus much ; that the nerves also pass into the pulp, and may even be easily seen on the pencils of arteries, and finally that they disappear as very small branches of not greater size than the smallest capillaries ; but I am unable to decide whether they terminate by means of loops or with free extremities. In the calf, the thickness of these smallest nerves on arteries of a line in diameter (where it is not uncommon to find two such trunks) is 21 to 28-1000ths of a line ; on the pencils of arteries 48 to 56-10,000ths ; on the smallest ar teries and capillaries 3 to 4-1000ths. Their structure was so far peculiar, that in the calf the finest nerves (fig. 539.) exhibited no trace of nerve fibres, even when treated with soda and acetic acid, but they seemed to consist wholly and solely of the fibres of Remak. Nevertheless, in branches of 12 to 28-1000ths of a line, I have often very plainly seen a single nerve tubule of 20 to 28-10,000ths of a line (fig.540.), with dark margins, in the midst of the fibres of Remak. From these facts it may be concluded that the finest nerve tubes in the spleen of the calf are devoid of the dark bor ders, just as they are in the organ of smell according to Todd and Bowman ; or as in the Pacinian corpuscles, the cornea, &c. ; but we are scarcely able to conclude therefrom that they possess the same constitution in the adult animal. I will here permit myself to add an interesting microscopic observation concerning the splenic nerves of the calf. A division of the primitive nerve fibres takes place in them (fig. 541.), similar to that which Henle and myself found in the Pacinian cor puscles, Milller, Briicke, and R. Wagner in the muscles, and Savi and R. Wagner in the electrical organ of the torpedo. But what is altogether new in the minute anatomy of nerve is, that these divisions do not take place at the terminations of the primitive nerve fibres, but in their trunks. I detected them in the large trunks which accompany the splenic artery previously to its entering the hilus ; and, indeed, in considerable numbers, so that I often counted three or four such divisions in one preparation. They always took place by the division of a primitive nerve fibre at an acute angle into two parts, and never gave rise to more fibres. These divisions often repeated themselves on the same fibre, so that in one instance three, and in another case even four, fibres were given off by the successive divisions of a single primitive fibre: this happened in the smaller branches in the interior ; but, so far as I could remark, it did not occur in the smallest branches of nerves, although, from the difficulty of examining the finer nerves, I cannot say that such divisions were absolutely wanting here. The significa tion of these facts seems to be very important, both in an anatomical and physiological point of view, but this is not the place to give a more detailed statement. But thus much will I remark : that by means of such a dis tribution of the nerves, a small nerve may be rendered subservient to a larger organ ; and, in addition, an harmonious activity of the whole organ may be facilitated ; while, finally, in respect to sensation, it may possibly ex plain the want of an exact local sensibility.