In concluding this treatise on the anatomy of the spleen, I will allow myself brief 1 y to propound somewhat concerning the physio logical and pathological properties of the organ.
The spleen is developed at the end of the second or the beginning of the third month, in the fcetal mesogastrium at the fundus of the stomach. It originates from a blastema which is developed independently in this situation, and neither proceeds from the intestine, like that of the liver, nor from the pancreas, as Arnold has maintained ; since, although in the ruminants it is placed on this gland, yet in the dog, according to Bischoff; it is not. It is at first a small, white, often slightly lo. bulated corpuscle, which gradually reddens, and soon becomes as rich in vessels and blood as it is in the adult. The elements of the fcetal spleen are originally quite uniform cells ; at a later period part of these are transformed into fibres and vessels, while part become persistent as the parenchyma-cells. It is only subsequently that the Malpighian corpuscles are developed, yet I have found them, without exception, both in man and animals, at the end of the fcetal life. Ac cording to Heusinger, the proportion of the spleen to the whole body is, in an embryo of ten weeks old, as 1 to 3000 ; in the eighth month it is, according to Huschke, as 1 to 720 ; while at birth, he states it to be as 1 to 357 ; in the adult as 1 to 235 to 400 ; and in old age as 1 to 600 to 800. From these data it will be seen, that the proportionate weight of the spleen to that of the whole body in creases very rapidly in the embryo, and is almost as great at the period of birth as in the adult ; from which it sufficiently follows, that the spleen is an organ, the activity of which extends from the end of the fcetal period through the whole life, and reaches its highest point in middle age.
As regards the function of the spleen, of the innumerable theories and hypotheses re specting it, only a very few deserve a nearer consideration ; namely, only those which place the spleen in intimate relation with the life of the blood. In point of fact, almost all the facts which with greater or less certainty we know concerning the spleen, and, above all, the ana tomical ones, point to such a relation. Hew son had already stated, that when an organ receives more blood than it requires for its own nutrition, we may conclude therefrom that that blood undergoes a change in it, or a secretory process takes place ; and this ex pression will not apply to any organ in the body better than to the spleen, which must be considered as relatively better supplied with blood than any other organ. Therefore since all pathological, anatomical, and physiological facts prove a relation of the spleen to the blood, we may securely assume, that a change of the blood takes place in the spleen. The only difficulty is to know what change. Firstly, the blood may either suffer a change in its transition from the arteries to the veins ; or, secondly, the separation of a particular lymph from the blood may take place in this organ. It is well known that the latter view was first maintained by Hewson *, who at the same time announced that the lymph generated in the spleen serves to form blood corpuscles ; and since then, Tiedemann and Gmelin have specially supported the same view. But the grounds adduced for this theory seem to me to be insufficient. At one time, the great quan tity of lymphatics in the spleen was brought to prove that a special lymph was developed here. But that part of the spleen on which
special stress is laid, namely, the interior or parenchyma, is quite poor in lymphatic vessels ; and its surface, even in the lower animals, scarce contains more of such vessels than other organs ; to wit, the peritoneum covering the liver, the pleura covering the lungs, &c. Therefore the formation of a special lymph by the spleen can as little be assumed as in the case of the lungs and liver. Se condly, the red colour of the spleen-lymph, .anc1 its greater coagulability, have been ad duced as proofs of a peculiarity, and of a blood-forming import. But it may be de manded, are these properties constant, and on what do they depend ? As to the first ques tion, it is certain that a red colour of the spleen-lymph is, on the whole an exception, as Seiler and Ficinus # formerly stated. In rabbits, cats, or dogs, I have never found such a colour, and have also always found the chyle of the thoracic duct of only different shades of white. But I will not deny that in calves and sheep a reddish spleen-lymph is often found, and I will add that this is frequently the case in the horse. But this is sometimes the case in other organs, as, for instance, in the liver and in the lacteals, where Tiedemann and Gmelin in some cases also found a reddish and very easily coagulable fluid; and it is im portant to observe, that the reddish colour and easy coagulability in these cases depend simply on blood which is mixed with the lymph. Thus, if the reddish spleen-lymph of a calf be examined, a quantity of fully de veloped blood corpuscles are found in it, which are altogether identical with those in the blood,f Now since it cannot be as sumed that real coloured blood globules are formed in the lymphatic vessels of the spleen, and since, in point of fact, all trace of such a developement of blood globules is absent, it will only follow from the facts adduced, that in the cases of reddish spleen-lymph a mixture of real blood and lymph has taken place. This mixture may be the result of normal anas tomoses between lymph and bloodvessels, or may owe its origin to a rupture of both these vessels. I believe the latter to be the case, and am simply of the opinion that it is not at all to be wondered at. For in Tiedemann's cases the animals were either killed by a blow on the head, or died during convulsions ; and it is not surprising that during such a death struggle an organ so richly supplied vsith blood as the spleen should make an abnormal path for that fluid, or that a similat thing should happen when the vena porta has been tied. It is well enough known, how easily the lymphatics of the spleen are filled by an injection into the bloodvessels. The reddish colour and easy coag,ulability of the spleen lymph in particular cases therefore proves nothing at all, except that, on account of its great vascularity, blood is more easily extra vasated in the spleen than elsewhere, and enters the lymphatic vessels. Thirdly and lastly, Tiedemann and Gtnelin adduce the above-mentioned course of the lymphatics in the tortoise as a powerful proof of their view ; but Rudolphi $ found exactly the contrary, since in two large sea-tortoises not a single lymphatic of the intestine passed to the spleen, but they all went directly to the thoracic duct.