CHAP, iv.] THE VASCULAR MECHANISM. 339 



is further shewn by the fact that if in the frog, an artificial blood 

 of normal saline solution to which milk has been added be substi- 

 tuted for normal blood, a stasis may by irritants be induced in 

 which oil-globules play the part of corpuscles, and by their aggre- 

 gation bring about an arrest of the flow. 



We are driven to conclude that there exist in health certain 

 relations between the blood on the one hand and the walls of the 

 vessels on the other, by which the tendency of the corpuscles to 

 adhere to the blood vessels is kept within certain limits ; these 

 relations consequently determine the normal flow, with its axial 

 stream and peripheral zone, and the normal amount of peripheral 

 resistance ; in inflammation, these relations, in a manner we 

 cannot as yet fully explain, are disturbed so that the tendency 

 of the corpuscles to adhere to the sides of the vessels is largely 

 and progressively increased. Hence the tarrying of the corpuscles 

 in spite of the widening of their path, and finally their agglomera- 

 tion and fusion in the distended channels. 



We may add that the changes occurring in the vascular walls 

 also at least facilitate the migration of the corpuscles, and modify 

 the passage from the blood to the tissue of the fluid parts of the 

 blood, the lymph of inflamed areas being richer in proteids than 

 normal lymph. 



We must not however pursue this subject of inflammation any 

 further. We have said enough to shew that the peripheral resis- 

 tance (and consequently all that depends on that peripheral 

 resistance) is not wholly determined by the varying width of the 

 minute passages but is also dependent on the vital condition of 

 the tissue of which the walls of the passages form a part. When 

 the tissue is in health, a certain resistance is offered to the 

 passage of blood through the capillaries and other minute vessels, 

 and the whole vascular mechanism is adapted to overcome this 

 resistance to such an extent that a normal circulation can take 

 place. When the tissue becomes affected, the disturbance of the 

 relations between the tissue and the blood may, as in the later 

 stages of inflammation, so augment the resistance that the passage 

 of the blood becomes at first difficult and ultimately impossible. 

 And it is quite open to us to suppose that under certain circum- 

 stances the reverse of the above may occur in this or that area, 

 conditions in which the resistance may be lowered below the 

 normal, and the circulation in the area quickened. Thus the 

 vital condition of the tissue becomes a factor in the maintenance 

 of the circulation ; and it is possible, though not yet proved, that 

 these vital conditions are directly under the dominion of the 

 nervous system. 



185. Changes in the peripheral resistance may also be 

 brought about by changes in the character of the blood, especially 

 by changes in the relative amount of gases present. When a 

 stream of defibrinated blood is artificially driven through a 



222 



