THE CAPILLAKY CIRCULATION. 233 



examination. They probably thus adhere by virtue of the amoeboid move- 

 ments of their protoplasm, so that the adhesion is to be considered not so 

 much a mere physical as a physiological process, and hence may be expected 

 to vary with the varying nutritive conditions of the corpuscles and of the 

 bloodvessels. Thus while the appearance of the white corpuscles in the 

 peripheral zone may be due to their lightness, their temporary attachment 

 to the sides of the vessels and characteristic progression is the result of their 

 power to adhere ; and as we shall presently see, their amoeboid movements 

 may carry them on beyond mere adhesion. 



168. These are the phenomena of the normal circulation, and may be 

 regarded as indicating a state of equilibrium between the blood on the one 

 hand and the bloodvessels with the tissues on the other; but a different state 

 of things sets in when that equilibrium is overthrown by causes leading to 

 what is called inflammation or to allied conditions. 



If an irritant, such as a drop of chloroform or a little diluted oil of 

 mustard, be applied to a small portion of a frog's web, tongue, mesen- 

 tery, or some other transparent tissue, the following changes may be ob- 

 served under the microscope ; they may also be seen in the mesentery or 

 other transparent tissue of a mammal. The first effect that is noticed is a 

 dilatation of the arteries, accompanied by a quickening of the stream. The 

 irritant, probably by a direct action on the muscular fibres of the arteries, 

 has led to a relaxation of the muscular coat and hence to a widening ; and 

 we have already ( 112), explained how such a widening in a small artery 

 may lead to a temporary thickening of the stream. In consequence of the 

 greater flow through the 'arteries, the capillaries become filled with corpus- 

 cles, and many passages, previously invisible or nearly so on account of 

 their containing no corpuscles, now come into view. The veins at the 

 same time appear enlarged and full. If the stimulus be very slight, this 

 may all pass away, the arteries gaining their normal constriction and the 

 capillaries and veins returning to their normal condition ; in other words, 

 the effect of the stimulus in such a case is simply a temporary blush. 

 Unless, however, the chloroform or mustard be applied with especial care 

 the effects are much more profound, and a series of remarkable changes 

 sets in. 



In the normal circulation, as we have just said, white corpuscles may 

 be seen in the peripheral, plasmatic zone, but they are scanty in number, 

 and each one after staying for a little time in one spot suddenly gets free, 

 sometimes almost by a jerk, as it were, and then rolls on for a greater or 

 less distance. In the area now under consideration a large number of white 

 corpuscles soon gather in the peripheral zones, especially of the veins and 

 venous capillaries (that is, of the larger capillaries which are joining to 

 form veins), but also, to a less extent, of the arteries ; and this takes place 

 although the vessels still remain dilated and the stream still continues 

 rapid though not so rapid as at first. Each white corpuscle appears to ex- 

 hibit a greater tendency to stick to the sides of the vessels, and though 

 driven away from the arteries by the stronger arterial stream, becomes 

 lodged, so to speak, in the veins. Since new white corpuscles are continu- 

 ally being brought by the blood-stream on to the scene, the number of them 

 in the peripheral zones of the veins increases more and more, and this may 

 go on until the inner surface of the veins and venous capillaries appears 

 to be lined with a layer of white corpuscles. The small capillaries, too, 

 contain more white corpuscles than usual, and even in the arteries these 

 are abundant, though not forming the distinct layer seen in the veins. The 

 white corpuscles, however, are not the only bodies present in the peripheral 

 zone. Though in the normal circulation blood-platelets (see 33) cannot 



