ii8 Disturbances of Circulation. 



Stasis and stagnation of the blood may at times be caused by substances 

 which act by inducing a withdrawal of the fluid elements and thus a 

 thickening of the blood (chemicals acting upon vessel walls). [This can 

 well be shown experimentally by bathing the mesentery of a frog, arranged 

 for demonstrating the blood current, with a hypertonic saline solution, a 

 rapid exosmosis of fluid taking place and the current being soon entirely 

 checked, with the vessels choked with corpuscles.] 



Deficiency of blood in an organ may be part of anaemia 

 of the general body (general oligsemia or an?emia ; d priv., 6\lyos, 

 little, and al/xa, blood) or a consequence of local impediment to the 

 blood current (local anaemia, ischaemia, from taxeiv, to limit or 

 check). The blood supply to any part mdy be impeded by: 



1. Pressure upon the part (coniprcssion aiuvniia) from in- 

 crease in. the bulk of adjacent organs, accumulations of fluid or any 

 other compressing influence upon the part from without, or by nar- 

 rowing of the capillaries by fat deposit, fluid or air in the paren- 

 chyma of the organ. 



2. Narrowing, occlusion or fault of contractility of the arteries. 

 Here may be mentioned external pressure upon the vessel, ligation, 

 occlusion by solid bodies as by thrombi in the arterial lumen (cf. 

 thrombosis and embolism) , rigidity of the vascular walls from cal- 

 cification or sclerosis and spasm of the arterial musculature with 

 resultant contraction of the lumen {arterial ancemia or ischccmia, 

 occlusion ancrmia, spastic ancemia). 



3. In addition, anaemia may involve a certain part of the body 

 in case the general blood distribution is irregular because the gen- 

 eral volume of blood passes to one large area to the deprivation 

 of other parts (collateral ancrmia); as when the posterior parts of 

 the body are markedly infiltrated with blood (symptomatic 

 anthrax) the fore parts are rendered ansemic, or as when interna! 

 haemorrhages occur the flesh is left ansemic, etc. 



The organ or tissue deprived of its blood looks pale, the absence 

 of the blood tint permitting the peculiar hue to become more appar- 

 ent and more like the tissues of slaughtered animals or like a 

 washed tissue deprived of its blood by the washing. It contains 

 less fluid and but little blood appears on the sectioned surface, and 

 its volume is diminished because of the emptiness and collapse of 

 the vessels. 



Ansemic parts at the exterior of the body, being exposed to the 

 air and losing their heat, feel cool, because with the loss of blood 

 their principal thermal substance is lost and they are capable of 

 producing little or no heat in themselves under the circumstances ; 



