INFLAMMATION. 165 



themselves and to absorb a larger quantity of matter than usual, and to 

 transform it according to circumstances. It also alters the relations of 

 the cells to the neighbouring parts, whether blood-vessels or other 

 structures. 



Inflammation may be said to have begun from the moment that this 

 increased absorption of matters into the tissue takes place, and the fur- 

 ther transformation of those matters commences. 



329, Causes of irritation. 



All irritation may in a certain sense be said to be dependent on the 

 nervous system. An external blow, for instance, produces irritation and 

 pain through the medium of the nerves of the part. Nerves may, how- 

 ever, produce irritation and pain from causes other than external. 



Hence the irritation in the tissue, which produces its altered vital 

 action, may in general language be said to be due to nervous influences. 

 Much that concerns the nervous system, and the causes and agencies 

 which influence it, is still a sealed book to the medical inquirer. We 

 know, however, that many causes elevate it, whilst others depress it, 

 and some even to the extent of paralysis. We know also that prostra- 

 tion generally supervenes very rapidly on nervous excitement. This 

 latter fact is very important in regard to the nature and treatment of 

 inflammation. 



330. Effect of irritation on the part affected. 



The part directly affected by the irritation is the tissue itself. The 

 blood is only indirectly affected from the changes which occur in the 

 performance of function in the tissue. The cells under the influence of 

 irritation, or in other words under the influence of the disturbance of 

 their normal functions, absorb and appropriate material from the blood 

 in greater quantity and in an altered way to what they would do in 

 health ; and again they transform the material so taken up into matters 

 different to what they would do in health. Hence the nutrition of the 

 part is altered, — it may be increased or it may be diminished ; and as a 

 further result, the condition of the other tissues connected with the part 

 is also altered. 



Among other results of the functional disturbance in the tissue is an 

 alteration in the character of the blood. 



331. Phenomena of inflammation. 



Before proceeding further, we must turn aside for a moment to consi- 

 der the phenomena of inflammation. The various changes in the circu- 

 lation of the part are well seen on irritating the transparent vascular 

 membrane of the web of a frog's foot. The first effect is contraction of 

 the channels of the smaller vessels and increased rapidity of the circula- 

 tion. 2ndly. The same vessels become enlarged, and the current of 



