501 



arranged, the glass plate is laid on the stage of the microscope, and the 

 mesentery examined with lenses of different powers, according as is 

 found necessary. It is not needful to apply any irritant to the mesen- 

 tery, for the mere contact with the air is sufficient to excite a severe 

 suppurative peritonitis ; and as the animal often lives and the circula- 

 tion goes on steadily for upwards of forty-eight hours, the inflammation 

 can be watched with great facility in all its stages. 



In a mesentery so exposed the following phenomena are observed. 

 The blood vessels dilate. The arteries dilate at first, and with considera- 

 ble rapidity; next the veins, more slowly. These vessels are some- 

 times enlarged to double their former diameter. The capillaries dilate 

 less ; their apparent increase in size being chiefly due to their contain- 

 ing a greater number of red corpuscles, and so becoming more distinct. 

 Coincidently with this vascular dilatation a slowing of the course of the 

 blood is seen to occur, and the white corpuscles appear more nume- 

 rously in the peripheral layers of blood in both arteries and veins, but 

 more particularly in the latter. The white corpuscles go on accumulating 

 along the sides of the veins, and become stationary, adhering to the vas- 

 cular wall, till at last the inner surface of each vein is lined by a conti- 

 nuous layer of white corpuscles, forming a secondary tube, in the centre 

 of which the ordinary current continues to flow. Shortly after this 

 small projections are seen on the outer surface of the veins, and these 

 gradually enlarge till they each attain the size of a white blood cor- 

 puscle, which they further resemble in colour and granular appearance. 

 At last they are attached to the wall of the vein merely by a narrow 

 stalk; and from the side remote from the vessel they begin to throw out 

 finger-like processes and to perform other amoeboid movements, till at 

 length the stalk separates from the vein, and the corpuscle becomes free, 

 moves away, a perfect pus corpuscle, into the tissue of the mesentery. 

 This emigration of corpuscles goes on from all sides of the vein till the 

 vessel is surrounded by a thick mass of cells which have passed out 

 through its walls, and which were white blood cells, but which, now 

 they are extravasated in an inflamed tissue, must be called pus or exu- 

 dation cells. They undergo the most remarkable alterations of form, 

 and spread themselves through the tissue and over the surface of the 

 mesentery by virtue of the power of spontaneous motion enjoyed by all 

 masses of living protoplasma. In the capillaries during this time the 

 circulation is very irregular. In some vessels it continues to flow un- 

 intermittingly in a continuous stream. From such a capillary no emi- 

 gration of corpuscles takes place. In other vessels the current stagnates 

 for a time, and again goes on. In others the stagnation is permanent, 

 and in some the current varies from time to time both in direction and 

 rapidity. In those vessels in which a stoppage of the blood flow occurs, 

 whether temporary or permanent, the exit of the corpuscles can be ob- 

 served with great clearness. The white cells, which when in circula- 

 tion always preserve the spherical shape, when they come to rest inside 

 the vessel begin to change in form, and after a little time they are seen 

 to pass through the wall of the capillary just as they do through that 



