INFLUENCE OF IRRITATION. 299 



phenomena which follow their application are necessarily 

 very complex. The process of inflammation is by no means 

 completely understood, but it is pretty generally acknowl- 

 edged to be a modification of nutrition, in a way that we are 

 as yet ignorant of. We are hardly prepared to admit that 

 this modification, whatever it may be, can be induced under 

 our very eyes, simply by the application of irritants. With 

 these views, microscopic researches on the " state of the blood 

 and blood-vessels in inflammation " do not assume the im- 

 portance which is attributed to them by many authors. 



Keeping this in mind, we may state the following as a 

 summary of the phenomena which have been observed in 

 the capillary circulation, as the result of irritation applied to 

 transparent parts : 



The application of the irritant is immediately followed by 

 constriction of the arterioles, and diminution in the rapidity 

 of the current in them as well as in the capillaries. 



This constriction of the vessels is but momentary, if a 

 powerful irritant, like a very strong solution of salt, be used. 

 It is followed by a dilatation of the vessels, and an increase in 

 the rapidity of the circulation. 



Soon after the vessels have become dilated, the rapidity 

 of the circulation is progressively diminished, until oscillation 

 of the blood in the vessels takes place, which occurs when 

 the circulation is about to cease. This oscillation finally 

 gives place to complete stagnation. The vessels become 

 crowded with blood, so that the transparent layer next 

 their walls is no longer observed. In this condition, it has 

 been often noticed that the proportion of colorless corpuscles 

 is increased. 



Following the contraction and subsequent dilatation of the 

 vessels, there is stasis, and engorgement of the parts which 

 have been exposed to irritation. If the irritation be discon- 

 tinued, this condition is gradually relieved, and the blood re- 

 sumes its normal current. 



In inflammation, as it is observed in the conjunctiva and 



