124 Disturbances of Circulation. 



yet in capillary diapedesis from a mucous membrane, as the gastric 

 or intestinal lining, the points of escape are invisible to the naked 

 eye, and only the blood deposit on the surface and the pallor of the 

 mucous membrane indicate the fact of extravasation. Arterial 

 haemorrhages are recognized in living animals by the bright red 

 color of the arterial blood, by the spurting character of the escaping 

 stream from the larger arteries, the spurts corresponding to the 

 cardiac contractions ; while the bleeding from the veins is con- 

 tinuous and without pulsation. However, an arterial spurting may 

 be prevented by the interposed parenchyma (Samuel). If the larger 

 vessels between the point of haemorrhage and the heart be com- 

 pressed the haemorrhage will diminish if it be arterial ; it will be 

 increased if venous. 



The results of hcoiwrrJiage depend upon the quantity and the 

 duration of the bleeding, as well as the location of the lesion. In 

 case of loss of over one-third of the total volume of blood (about 

 3 to 4 per cent, of the body w^eight ; the average total quantity 

 being from one-tenth to one-twentieth of the weight of the body), 

 the flow continuing, the blood pressure falls. The vessel walls, 

 although capable of wide adaptation to the volume of blood within, 

 have become too wide for the diminished amount and cannot longer 

 advantageously propel it. A general oligaemia has been established, 

 indicated by the pallor of the mucous membranes, dizziness, faint- 

 ing (^an^mia of the brain) and convulsions, and the animal may 

 bleed to death. These results occur not only when the haemorrhage 

 is external, but also in copious haemorrhages into the intestinal 

 lumen, peritoneal cavity, etc. (internal haemorrhage). 



Haemorrhage gradually ceases by the closure of the opening in 

 the vessel from the formation of a blood coagulum in the opening 

 (adhesion thrombus), the closure being facilitated by constriction 

 of the vascular lumen (contraction of the wall), external pressure 

 (by the tissue engorged with blood), and by the fall of blood 

 pressure. After such cessation the volume of the fluid portion of 

 the blood is soon restored. The watery element first passes into 

 the vessels from the tissues and for a time the blood is conse- 

 quently more fluid (hydraemic) than before the haemorrhage; but 

 gradually the blood cells, regain their normal numbers as their 

 regeneration (cf. chapter on regeneration) proceeds in the blood 

 forming organs. 



At the site of haemorrhagic infiltrations the tissues present more 

 or less functional alteration. The presence of the extravasated 



