ORGANS OF THE BODY. 435 



their venous nature by means of injections, and it was from my prepara- 

 tions that Billroth became acquainted with them. Their diameter is, on 

 an average, 0'0169-0'022G mm., with extremes of 0-0113 and 0'02S2 

 mm., and their structure precisely the same as in the sheep. A spleen of 

 this kind, on the whole, presents, in regard to its pulp, great similarity to 

 the medullary mass and medullary passages of lymphatic glands. 



Here too, as in the sheep and all other mammals, the walls gradually 

 assume a more and more interrupted character, by separation of their 

 vascular cells, and thinning down of their cribriform substratum, so that 

 clefts leading into the bounding pulp-cords are formed. Finally, diminished 

 to 0'015S-0'0099, all the cavernous veins conduct the blood everywhere 

 into the venous radicles with their fissured Avails and defective vascular 

 cell-lining. 



233. 



Having now followed the cavernous venous passages down to their 

 finest subdivisions, the lacunar venous radicles, bounded only by the 

 tissue of the pulp, we next come to the important question so much dis- 

 cussed within the last few years, namely, How does the blood from the 

 ultimate ramifications of the arterial system find its way into the radicles 

 of the venous ? 



Many observers, among whom Gray, Billroth, and Koelliker may be 

 mentioned, believe that fine terminal capillaries open immediately into 

 the cavernous veins without having formed previously any true network. 

 Schiveigger-Seidel supposes the transition to take place through peculiar 

 vessels formed of fusiform cells alone. The views, however, of Key and 

 Stieda are quite different. According to them, there exists between the 

 capillary ramifications of the arterial system and the cavernous veins an 

 exfremely dense network of most delicate capillary vessels with distinct 

 walls, in whose tiny meshes the lymph oid cells are entangled, and which, 

 in broad terms, constitute the pulp. 



Many of these views are based upon the appearances produced by 

 incomplete injection or improper interpretation of preparations good 

 enough in themselves. 



Thus it not unfrequently happens that we believe we see direct open- 

 ings of capillaries into veins, which prove, on closer inspection, to be in 

 almost all cases optical illusions. 



We do not wish,, however, to characterise these immediate transitions 

 as impossible. We have, indeed, ourselves, during a long study of the 

 subject, met with appearances hardly capable of any other interpretation ; 

 but their number was extremely small, so that the conclusion that they 

 were only exceptional was forced upon us. Our own studies, therefore, 

 compel us to dissent from the opinion of Gray, Billroth, and Kodliker on 

 this point. 



Key and Stieda, on the contrary, have determined the true mode of 

 transition, but have mistaken an extremely dense reticulum of very delicate 

 lacunar passages for a network of capillaries possessed of distinct Avails. 



The fact is, that the passage of the arterial blood of the spleen into 

 the veins of the latter takes place in man and the mammalia generally in 

 small streams, having no special bounding walls. The blood traverses 

 the network of the pulp and interstices of the lymphoid cells contained in 

 the latter in the same manner if we may be allowed the comparison 

 as the water of a swelling river finds its Avay through the pebbles of its 



