ORGANS OF THE BODY. 431 



much more unfavourable circumstances than when dealing with animals, 

 namely, long after the death of the individual, and not unfrequently in 

 cases where death has been produced by protracted illness. Neverthe- 

 less, we may easily satisfy ourselves as to the infiltration of the arterial 

 sheaths, the local thickenings giving rise to follicular masses, and the 

 analogous arrangement of the finer blood-vessels. 



231. 



On passing beyond the lymphoid infiltrated investments, and also the 

 follicles, the arterial twigs continue their course for a certain distance 

 ramifying in the manner already described, but without any intercom- 

 munication among their branches. 



Finally, they are resolved into a multitude of straight capillaries which 

 anastomose only to a very small extent with one another. These are of 

 rather fine calibre, and are not unfrequently very tortuous also. They 

 pass on, taken as a whole, eventually into the finest vascular passages 

 of the pulp. 



Among the various mammals, however, the minute structure of these 

 capillaries differs considerably. In the pig, the dog, the cat, and the 

 hedgehog, most of them are (according to Schweigger-Seidel, Muller) 

 enveloped in elliptical swellings of the adventitia. These "capillary 

 husks" as they have been named by Schweigger-Seidel, which are of 

 great frequency among the capillaries of the spleens of birds (Muller) con- 

 sist of a pale, soft, and very finely granular mass, in which numerous 

 delicate nuclei are imbedded. Their dimensions in the dog, cat, and 

 hedgehog, are 0'0451-0'OGOO mm. in breadth, and 0-0902-0-1489 mm. 

 in length. The capillaries, enclosed either singly or in greater number 

 in these husks, present the same two-fold constitution of their walls, 

 already described in the foregoing section. Other capillaries of the same 

 animals just mentioned do not, however, show these husks, and corre- 

 spond thus with capillaries of man and the rest of the mammalia. 



The latter present for the most part a strong wall, as far as their transi- 

 tion into the vascular passages of the pulp, while some of them are seen 

 to be more delicate, more richly nucleated, or as though formed of single 

 apparently distinct vascular cells. 



Great variety, however, is seen among the lymphoid adventitise of such 

 capillaries. They may appear to be made up of a delicate mass of con- 

 nective substance, with round or elongated nuclei in the nodal points or 

 interstices, but may also become thicker, obtaining a more or less ribril- 

 lated coat of connective-tissue externally, with a more loosely reticular 

 portion internal to it, in whose interstices lymphoid and fusiform cells are 

 situated; thus reminding us of the "capillary husks" between which 

 and these there are intermediate forms. 



In possession of these points regarding the structure of the capillaries, 

 we may now at last turn to the consideration of the pulp. This is found 

 to be a very soft red mass, occupying all the interstices of the organ 

 between the partitions, vascular sheaths, follicles, and those other consti- 

 tuents already described. Its coarser and more minute structure is only 

 recognisable after artificial hardening. 



The pulp is made up of a nehcork of irregularly formed cords and 

 bands of a medium diameter of 0'0677-0'0226 mm. (fig. 420, &), which 

 bound a system of spaces and cavities varying again according to the 

 species of animal, but in every case designed for the reception of the 



