ON THE EARLY STAGES OF INFLAMMATION 228 
which this source of fallacy was carefully avoided, the variations in the calibre 
of the vessels being generally either induced by operations on the cord, or else 
such as occurred spontaneously. 
In a perfectly healthy state of the web with the heart beating powerfully, 
when the arteries are of about medium width, the current of blood in them 
is so rapid that the individual corpuscles cannot be discerned ; but in the capil- 
laries, whose aggregate calibre is very much greater than that of the arterial 
trunk which feeds them, the flow is so much slower that they can be pretty 
clearly distinguished. When the arteries are fully dilated, if the heart con- 
tinues to act with the same energy, the blood appears to move as rapidly in 
them as before, though of course in much larger quantity ; while in the capillaries 
the flow is extremely accelerated, so that it becomes as impossible to see the 
blood-corpuscles in them as in the arteries. On the other hand, when the 
arteries are considerably constricted, the blood moves more slowly through the 
capillaries than when the tubes of supply are of medium size, and at the same 
time the narrowed arteries appear to filter the blood more or less of corpuscles, 
which are found in smaller numbers in proportion to the liquor sanguinis in the 
capillaries: and if the constriction of the arteries is sufficiently great, the web 
is rendered quite pale in consequence of the small number of corpuscles in it, 
which nevertheless continue to move among the tortuous capillaries, producing 
in the field of the microscope an appearance something like that of a few flies 
playing about in a room. Finally, if the arteries are completely constricted, 
all appearance of flow in the capillaries vanishes, and the web has a wholly 
exsanguine aspect. Under these circumstances, even the veins, though still of 
large calibre, may contain little besides colourless liquor sanguinis, which has 
continued to ooze through the contracted arteries when the corpuscles have 
been completely arrested ; and so inconspicuous do the veins become in con- 
sequence of this change in the quality of their contents, that it may be extremely 
difficult to distinguish them from other tissues; the appearance of the web 
on superficial observation being as if it possessed no blood-vessels at all. This 
remarkable condition, which, so far as I know, has not been before described, 
may last for several minutes in consequence of irritation of the cord, and in one 
case I observed it occur spontaneously, and continue for five minutes together. 
It appears to be comparable to the dead whiteness of the human fingers when 
benumbed with cold, or the perfect pallor of the cheek in faintness ; while 
blushing is no doubt caused by full dilatation of the arteries. 
Such, according to my experience, are the effects produced upon the circu- 
lation by changes of calibre in the vessels of a perfectly healthy web. The 
arteries regulate by their contractility the amount of blood transmitted in 
