502 



of the vein. In the case of the capillary the last doubt as to the iden- 

 tity of cells within and those without the vessel is removed ; for the 

 vascular wall is here so thin as to allow a white corpuscle to be partly 

 within and partly without at the same time, and a gradual transference 

 of the substance of the corpuscle from the part within to the part with- 

 out can be watched till at last the corpuscle has wholly passed through, 

 and moves off to make way for others. Through the capillary walls 

 the red corpuscles also pass in considerable number ; and there are few 

 more remarkable objects than a capillary in which the blood has been 

 for some time stagnant, and in which a number of red corpuscles have 

 got halfway through the wall when the circulation recommences. The 

 parts of the corpuscles within are then agitated by the current, and 

 sometimes actually torn away from their other halves which have got 

 through, and remain motionless outside the vessel. 



The exit of corpuscles through the walls of the arteries is insigni- 

 ficant, and seldom occurs except when a dilatation followed by a constric- 

 tion of the vessel allows a temporary or partial stasis of the blood to 

 occur. Bed corpuscles never pass through the walls of the arteries or 

 veins. 



After some hours the mesentery becomes cloudy and opaque, from 

 the number of cellular bodies mixed with fluid exudation from the ves- 

 sels, which are spread out on its surface or imbedded in its substance ; 

 the appearances are those of well-marked suppurative peritonitis, and 

 any one not knowing whence the cells are derived would have no hesi- 

 tation in calling them pus corpuscles. 



It appears from this description that the main condition for the 

 emigration of white corpuscles is, that they should have come to rest 

 at all events for a short time while within the vessels. The white cor- 

 puscles, as is known, are composed of protoplasma, that peculiar sub- 

 stance which forms the mass of all living cells, whether animal or 

 vegetable. This protoplasma, among many remarkable properties, pos- 

 sesses two which are of great importance in our present subject — 

 namely, irritability and the power of spontaneous movement. While 

 the blood is circulating, and while the corpuscles are being perpetually 

 rubbed against each other and against the sides of the vessels, the pro- 

 toplasma is kept in a condition of tetanus ; and, contracting so as to oc- 

 cupy the smallest possible space, it maintains the spherical shape of the 

 ordinarily described white blood cell, and in this condition it is incapa- 

 ble of passing through the walls of the vessels. But no sooner do the 

 corpuscles come to rest, and get relief from the perpetual irritation of 

 friction, than they begin to move, throwing out processes and changing 

 in shape just as some infusorial animals are seen to do ; hence, these 

 movements have been described and are usually known under the title 

 of the amceboid movements of the corpuscles. The white cells of the 

 blood further resemble the anraebain their power of taking up into their 

 substance minute particles of matter brought in contact with them; and 

 when the corpuscles are thus fed, as it were, with materials easily 

 recognisable, their passage through the vascular walls and their wan- 



