186 FORMAL HISTOLOGY. 



capillary hlood-pressure is increased or the pulp distended or the tra- 

 becular contract, these clefts open ; under other circumstances they 

 are closed and the circulating blood is confined to the vessels. The 

 vascular connection between what may be called the arterial capil- 

 laries and venous capillaries is a dilated capillary, or "ampulla," 

 larger than other capillaries, and it is in these ampullae that the endo- 

 thelium is composed of the narrowest spindle-shaped cells, so that 

 the clefts between them would be most pronounced in this part of 

 the vascular system of the organ. During life the spleen displays 

 slow rhythmic contractions at intervals of about a minute, and from 

 what has been said of its structure it will be obvious that these con- 

 tractions would favor the circulation of blood through its vessels and 

 pulp. It appears, indeed, that these contractions are essential, for 

 if the muscular tissues be thrown out of function by severing the 

 nerves, the circulation is so interfered with that the pulp becomes 

 engorged with blood. No lymphatic vessels have been discovered 

 in the spleen. 



The pulp consists of a fine reticulum of delicate fibres and cells, 

 with branching and communicating processes, in the meshes of 

 which there are red blood-corpuscles, leucocytes in greater number 

 than normally present in the blood, and free amoeboid cells consid- 

 erably larger than leucocytes, called the " splenic cells." 



The adventitia of the arteries contains considerable lymphadenoid 

 tissue, which after the exit of the vessels from the trabecular is 

 expanded at intervals to form spherical bodies, about 1 mm. in diam- 

 eter, called the " Malpighian bodies " or " corpuscles." These are 

 like little lymph-follicles, through which the artery takes its course. 

 The reticulum in these Malpighian corpuscles is scanty and incon- 

 spicuous near their centres, so that the lymphoid cells it contains 

 appear densely crowded ; but toward their peripheries the reticulum 

 is more pronounced and the cells a trifle more separated. At the 

 surface of the Malpighian body its reticulum becomes continuous 

 with that of the pulp surrounding it (Fig. 161). 



The relations between the spleen and the blood flowing through 

 it appear to be very similar to those between the lymphatic glands 

 and the lymph passing through them. It seems to act as a species 

 of filter, in which foreign particles or damaged red blood-corpuscles 

 are arrested and destroyed. In many infectious diseases the splenic 

 pulp is increased in amount and highly charged with granules of 

 pigment that appear to be derived from the coloring-matter of the 



