ON THE EARLY STAGES OF INFLAMMATION 219 
The sketch given below represents the calibre of an artery dividing into 
minute branches, with the capillaries into which they poured their blood. At 
the time when it was drawn, the artery and its branches were in a state of spon- 
taneous contraction, yet the capillaries retained their full average dimensions. 
After a while the artery became so much more contracted as only to admit 
single corpuscles even through the main trunk ; yet still the capillaries fed by it 
did not appear affected in calibre. This is but one example of what I have 
observed times without number. 
= 
ee 
The capillaries, though not contractile, are highly elastic, and by virtue of 
this property are capable of considerable variation in capacity, according to the 
distending force of the current of blood. Figs. 3 and 4 of Plate ITI (see p. 68), 
traced with the camera lucida, show, besides the pigment in two chromatophorous 
cells of the frog’s foot, part of a capillary in nearly extreme conditions in point 
of calibre. In Fig. 3 the vessel is about equal in diameter to the length of a red 
corpuscle, while in Fig. 4 it is so narrow that the corpuscles in it are pinched 
transversely and elongated. When the capillaries are most distended, their 
parietes are much thinner than when shrunk to their smallest dimensions ; 
an estimate may be formed of the difference by comparing the close proximity 
of the corpuscles to the outer bounding line of the vessel in Fig. 3 with the con- 
siderable interval in Fig. 4, that interval representing the apparent thickness 
of the wall of the vessel. It is to be observed that the frog had been killed in 
a manner involving considerable haemorrhage before Fig. 4 was traced, so that 
the capillaries were then little, if at all, distended with blood. The thinness 
of the walls of the capillaries, as compared with the small arteries, is, doubtless, 
calculated to favour the mutual interchanges which must take place between 
the blood in them and the tissues in their vicinity. 
It is believed by some eminent authorities that mutual attractions and 
repulsions subsisting between the nutrient fluid and the tissues among which it 
