220 CHANGES IN THE CAPILLARIES. [BOOK i. 



equilibrium which is the central fact of a normal capillary circula- 

 tion, of a normal interchange between the blood and the tissue, and 

 thus of a normal life of the tissue. The existence of this equi- 

 librium is best shewn when it is overthrown or modified, as in 

 inflammation and 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, a frog's 

 tongue, or some other transparent tissue, the following changes may 

 be observed under the microscope. The first effect that is noticed 

 is a dilation of the arteries, accompanied by a quickening of the 

 stream. The capillaries become filled with corpuscles, and many 

 passages, previously invisible or nearly so on account of their con- 

 taining no corpuscles, now come into view. The veins at the same 

 time appear enlarged and full. The increase of width is most 

 marked in the arteries, next so in the veins, and least of all in 

 the capillaries. If the stimulus be very slight, this may all pass 

 away, the arteries gaining their normal constriction, and the capil- 

 laries and veins returning to their normal condition; in other 

 words, the effect of the stimulus in such a case is simply a tem- 

 porary blush. Unless however the chloroform or mustard be applied 

 with especial care the effects are much more profound and lasting. 

 In the case of the frog's web a condition is set up known under the 

 name of stasis. This has been considered as merely a phase of in- 

 flammation, since in the frog's web in which inflammation has been 

 largely studied, the agents which produce inflammation frequently 

 produce stasis. But in the frog's tongue and elsewhere true inflam- 

 mation may be set up and produce all its results without any stasis 

 making its appearance; and though the two conditions are in 

 several respects similar, they appear to be distinct: stasis being the 

 result of the profounder action of the irritant and the forerunner of 

 local death or necrosis. 



It is this stasis which particularly illustrates the points to which 

 we wish to call attention. When as the result of the irritant, the 

 initial blush passes into stasis, the following events may be observed. 

 The quickening of the stream gives way to a slackening; this is 

 not due to any returning constriction of the arteries, for they still 

 continue dilated. It will further be observed that the red corpuscles, 

 instead of being in the larger capillaries and smaller arteries and 

 veins confined to the axial stream, are diffused and indeed crowded 

 over the whole width of the channels. The capillaries and veins 

 get more and more crowded with corpuscles, the white corpuscles 

 being scattered irregularly among the more numerous red ones; 

 and though the channels get wider and wider, becoming frequently 

 even enormously distended, the stream becomes slower and slower, 

 until at last the movement of the blood in the affected area ceases 

 altogether. The phase of accelerated flow has given place to stasis. 

 The capillaries, veins and small arteries are choked with corpuscles, 

 and it may now be remarked that the red corpuscles seem to run 



