MORPHOLOGY OF THE BLOOD 107 



Temperature. Cold retards coagulation. Gentle warmth, 40 C., hastens 

 but a temperature above 56 C. destroys clotting, since that temperature heat- 

 coagulates the fibrinogen. 



Contact with Foreign Bodies. Such contact hastens clotting. This is 

 due to the influence of such bodies on the formation of fibrin factors, es- 

 pecially the substances that arise from the disintegration of the leucocytes. 



Condition of the Blood-Vessel Walls. Intra vascular clotting often takes 

 place upon injury of the endothelial lining of the blood-vessel, probably 

 from the liberation of thrombokinase in quantity too great for elimination 

 by the healthy portion of the wall. The healthy endothelium no doubt is 

 an important factor in eliminating the small amounts of the fibrin factors 

 that must be constantly forming. The open wounds and lacerations of 

 tissue that accompany the loss of blood by accident are the very conditions 

 most favorable to clotting, since large amounts of tissue extract, thrombo- 

 kinase, are formed under these conditions. 



Neutral Salts. The addition of neutral salts in the proportion of 2 or 3 

 per cent and upward. When added in large proportions, most of these 

 saline substances prevent coagulation altogether. Coagulation, however, 

 ensues on dilution with water. The time during which salted blood can be 

 thus preserved in a liquid state, and coagulated by the addition of water, 

 is quite indefinite. 



Oxalates and Fluorides. These and other precipitants of calcium pre- 

 vent clotting by removing this substance. 



Peptone. The injection of commercial peptone in the blood-vessels of 

 an animal to the extent of 0.5 gram of peptone per kilo weight of the body 

 of the animal will deprive the blood of the power of coagulation. If a smaller 

 quantity be injected the coagulation of the blood will be delayed. If peptone 

 blood is drawn and centrifuged, the plasma obtained, which is called peptone 

 plasma, can be made to coagulate by diluting sufficiently with water and 

 letting it stand a long time. Peptone plasma in the blood-vessels of the ani- 

 mal gradually regains the power to coagulate. 



MORPHOLOGY OF THE BLOOD. 



The corpuscles floating in the fluid plasma of the blood, when separated 

 by a centrifugal machine are found to make up 45 to 50 per cent of the total 

 mass of the blood. These corpuscles, or formed elements, are of three 

 varieties, the red corpuscles or erythrocytes, the w r hite corpuscles leucocytes, 

 and the blood platelets which have been called thrombocytes . 



Red Corpuscles or Erythrocytes. Human red blood-corpuscles 

 are circular, biconcave discs with rounded edges, from 7 /j. to 8 p. in diameter, 

 and about 2 p. in thickness. When viewed singly they appear of a pale 

 yellowish tinge; the deep red color which they give to the blood being ob- 



