210 ON THE EARLY STAGES OF INFLAMMATION 
directed to the part by a feeling of uneasiness, will be that the skin is redder 
than natural, implying that the vessels are abnormally loaded with blood, and 
if the irritation be continued, the cuticle will be raised in the form of a blister. 
If, now, the loosened epidermis be artificially removed on the earliest occurrence 
of effusion, a scarlet raw surface will be exposed; and on pressing the tender 
dermis firmly with the finger, and suddenly removing the pressure, it will be 
found that while the redness will for the most part have momentarily disappeared, 
there will be many minute red points from which the blood cannot be expelled. 
This shows that, while the blood is in part still free to move, there are some 
minute vessels completely clogged with it. Again, if a portion of mustard be 
placed on the skin covering the dorsal aspect of one of the fingers, abnormal 
redness will very speedily be produced, which in the first instance disappears 
completely on pressure; but, if the mustard has been kept on long enough, 
can be only imperfectly dispelled ; and if the application be still longer con- 
tinued, vesication will be the result. I had lately the opportunity of examining 
the brain of a man who had died of tetanus, complicated with incipient meningitis; 
the post mortem appearance of the latter being maculiform congestion of the 
pia mater. Having stripped off a portion of the affected membrane, and care- 
fully washed away with a camel’s-hair brush the cerebral substance adhering 
to it, I applied the microscope to one of the affected spots, and found that all 
the minute vessels were filled with crimson blood, while those of the surrounding 
parts were comparatively pale. It was evident that the red corpuscles were, 
in the former, so closely crammed together as to produce the appearance of a 
uniform mass, while in the latter they were present only in their usual proportion 
to the liquor sanguinis. Thus it appears that in the human subject, inflamma- 
tion, whether induced by mechanical irritation or by an acrid application such 
as mustard, or of spontaneous origin, is characterized at an early period by 
a certain amount of obstruction to the progress of the blood through the minute 
vessels ; a phenomenon, which it is therefore of great importance to understand. 
It fortunately happens, that we have, in the transparent web of the frog’s 
foot, an opportunity of observing with the utmost facility the circulation of 
the blood in the living animal, and of watching the effects produced upon it by 
irritating causes. It may naturally appear very doubtful whether observations 
made upon creatures so low in the animal kingdom as the amphibia, can with 
propriety be brought to bear upon human pathology. A few facts will, however, 
suffice to show that no such doubts need be entertained. If a portion of mois- 
tened mustard be placed upon the web of a frog, tied out under the microscope, 
the blood-vessels will soon be found abnormally red; and if the application be 
continued long enough, all the capillaries will become choked with corpuscles so 
