THE BLOOD. 205 



The shape of the vessel is also a factor in the production of 

 "buffy coat." If the vessel be long and straight, the fall of the 

 corpuscles is facilitated. The huffy coat then appears. No buffi- 

 ness, however, is seen if the vessel be large and low, and if the blood 

 be received in a vessel which is shaken from time to time. The blood 

 of different parts of the vascular system shows differences as to the 

 time required for complete coagulation. Arterial blood coagulates 

 more quickly than venous; blood of the hepatic veins coagulates 

 very little, and the same is true of menstrual blood probably due 

 in the latter to mixture with the alkaline vaginal secretions, for, 

 when menstruation is so abundant that this alkalinity is overcome, 

 then clotting may ensue. 



Fibrinogen. This body pre-exists in circulating plasma. The 

 most recent experiments show that the liver is the place of origin 

 of fibrinogen, and many believe the myeloid tissue of the medulla 

 of the bones also participate in its formation. By different injuries 

 to the liver the fibrinogen disappears from the blood. The same 

 result ensues from poisoning by phosphorus and by chloroform, after 

 the injection of hepatotoxic serum, and after the exclusion of the liver 

 by Eck's fistula. After the arrest of the abdominal circulation the 

 fibrinogen disappears in the blood of the anterior part of the animal. 

 In most diseases with leucocytosis, also in irritation of the medulla of 

 bones, there is an hyperinosis, an increase of fibrinogen in the plasma. 

 But there is a direct relation between the number of leucocytes in the 

 circulating blood and the quantity of fibrinogen. 



With pneumococcus infection, according to Langstern and 

 Mayer, the formation of a leucocytosis is often attended with a 

 great increase of fibrinogen. 



The Change of Fibrinogen into Fibrin. It is supposed by Ham- 

 mersten that the thrombin causes a splitting of the fibrinogen mole- 

 cule, with the formation of an insoluble fibrin and a soluble fibrin- 

 globulin. The majority of observers do not believe in the splitting 

 of fibrinogen as held by Hammersten, but in a molecular change of 

 the fibrinogen. 



Agents which Retard Coagulation. Neutral salts, like concen- 

 trated solution of magnesium sulphate, sodium sulphate and sodium 

 chloride, retard coagulation. These salts retard the action of the 

 formed thrombin. Strong refrigeration acts in a similiar way. Bile 

 salts, in a much less concentrated solution than the neutral salts, 

 retard coagulation. The bile salts seem to do this in a way similar 

 to that of the neutral salts. Calcium chloride is often given for 



