THE THIRD HUXLEY LECTURE 523 



under irritation ? It was clearly not the result of direct action of the irritant 

 upon them. When the inllammatory congestion, as I ventured to term it, was 

 not carried to its extreme degree, the corpuscles, though closely packed, still 

 moving sluggishly along, successive portions of blood, as they passed through the 

 affected spot, were successively affected in the same way, it might be for hours 

 after the irritant had ceased to act. And some of the agencies which produced 

 the effect, such as gentle warmth and mechanical disturbance in the shape of 

 moderate pressure, were not of a nature to act chemically upon the blood- 

 cells, and could not possibly leave behind them among the tissues anv active 

 substance. 



The tissues, as distinguished from the blood, w'ere therefore the parts 

 primarily and essentially affected by the action of the irritant. And we have 

 seen that, in their relation to the blood-corpuscles, they approached more or 

 less closely, according to the degree of the irritation, the behaviour of ordinary 

 solids, such as glass, as distinguished from the living structures. The natural 

 inference was that they had lost more or less, for the time being, certain special 

 properties which they possessed when in active health as constituent structures 

 of the living body. In other words, certain of their vital functions were 

 temporarily in abeyance. I say temporarily because the extreme degree of 

 inflammatory congestion, in which the capillaries appear as homogeneous scarlet 

 threads of densely packed red discs, is susceptible of complete recovery by 

 resolution if the action of the irritant has not been pushed too far. 



The same conclusion followed naturally from a consideration of the pro- 

 perties of irritants. Greatly as they differ in their nature, whether physical, 

 as mechanical violence, heat, and the electric shock, or chemical of the most 

 varied characters, one feature they have all in common ; if pushed far enough 

 they destroy the tissues on which they act. Extreme inflammatory congestion 

 is the state which they produce when their action is just short of the lethal 

 degree ; and it could hardly be doubted that the state of the tissues just short 

 of death must be one of impairment of vital power. 



This view was beautifully confirmed by a series of observations to which 

 I was led by a most unlooked-for experience. Before I had adopted the method, 

 which I have described, of obtaining a perfectly tranquil state of the frog's 

 foot, I sought to study the local effect of an irritant b}' placing on the middle 

 of the web a small piece of moistened mustard, which could not be shifted in 

 position like a drop of liquid when the animal struggled. On removing the 

 mustard after a while to observe its effects, I was astonished to see the jiart 

 of the web on which it had lain, not only affected with inflammatory congestion, 

 but totally different in colour from the rest of the web in consequence of a dii- 



M m 2 



