REACTION 17 



Whatever their origin may be, they seem to play, as we 

 shall see, an important part in the process of coagulation. 

 They seem to be absent from avian and probably from 

 amphibian blood. 



The specific gravity of blood, measured by taking the specific 

 gravity of a mixture of chloroform and benzene, in which blood 

 neither rises nor sinks, varies in man between 1057 and 1066 — 

 slightly less in women. 



The viscositii, measured by its rate of flow through a capillary 

 tube, is five times that of water. It varies with the number of 

 red corpuscles. 



The amount of hcemoglobin is best measured by the Haldane- 

 Gowers Hsemoglobinometer. Blood diluted 200 times is saturated 

 with CO and the colour tested against a sample made up from a 

 mixture of blood (similarly treated) from a number of healthy 

 individuals. 



Proportion of Corpuscles to Plasma. — The proportion of corpuscles 

 to the total volume of blood is measured by the hematocrit. This 

 is a graduated tube, in which blood can be centrifugalised. The 

 corpuscles which settle at the bottom form normally about 37 per 

 cent, of the volume of the blood. 



Number of Corpuscles.- — This is estimated by means of the 

 Thoma-Zeiss hsematocytometer. 



REACTION OF THE BLOOD 



The reaction of the blood is most conveniently expressed 

 in terms of the concentration of hydrogen ions. Pure water 

 is very shghtly ionised into hydrions and hydroxyl-ions — 



H2O ;t H' + OHi . 



at 21° C. the concentration of H and OH being each 10 "'^ 

 gramme-ions per litre. If an acid such as HCl be added, this 

 is to a large extent dissociated into H- and CI -ions. The 

 H-ions in the system are therefore increased, let us say, to 

 10 " '^, the OH-ions being decreased, to a corresponding extent, 

 to 10"^. When an alkali is added the reverse takes place. 

 An acid is therefore a solution which has at 21° C. a H-ion 

 concentration greater than 10"'^, and an alkah is one 

 which has a H-ion concentration less than 10"'^. The differ- 

 2 



