126 THE BLOOD 



by the addition of water, is quite indefinite, if measures be taken to pre- 

 vent putrefaction. 



Oxalates and Fluorides. Oxalates to the extent of o.i per cent, con- 

 centration prevent clotting by the removal of calcium, one of the factors 

 in the formation of thrombin. Once thrombin is formed, clotting will 

 take place in the absence of soluble calcium. This is proven by the fact 

 that solutions of pure fibrinogen and thrombin form fibrin clots. 



Flourides, on the other hand, not only precipitate soluble calcium but 

 fix the blood platelets from which the prothrombin is formed. 



Peptone. The injection of commercial peptone (a mixture of proteoses 

 and peptones) in the blood vessels of an animal to the extent of o . 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 coagula- 

 tion of the blood will be delayed. If peptone blood is drawn and centri- 

 fuged, the plasma obtained is called peptone plasma. Howell has shown that 

 peptone contains antithrombin in a relatively large quantity. The increase 

 of antithrombin acts to restrain the reaction of prothrombin in the formation 

 of thrombin. Peptone plasma in the blood vessels of the animal gradually 

 regains the power to coagulate. When blood is drawn into a physiological 

 salt solution of proteose-peptone clotting occurs. 



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 white 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 j/j. to 8/* in diameter, 

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

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

 servable in them only when they are seen en masse. They are composed 

 of a colorless, structureless, and transparent filmy framework or stroma, 

 infiltrated in all parts by the red coloring matter, the hemoglobin. The 

 stroma is tough and elastic, so that as the corpuscles circulate they admit 

 of elongation and other changes of form in adaption to the vessels, yet 

 recover their natural shape as soon as they escape from compression. 



Number and Character of the Red Corpuscles. The normal number of 

 red blood-cells in a cubic millimeter of human blood was estimated by 

 Welcker, in 1854, to be 5,000,000 in men and 4,500,000 in women. Num- 

 erous recent observations, however, have shown that these estimates are a 

 little low, especially in men, and the average number has been placed by 

 different authorities at various points between 5,000,000 and 5,500,000. 

 Still the original numbers as given by Welcker are accepted at the present 



