234 THE BLOOD 



be thoroughly grasped. Where the amount of globulin in the 

 blood is increased, the chloride content increases, e.g. in pneumonia. 

 In patients with this infection, as well as in cases of chronic 

 nephritis and syphilis, the total protein content of plasma is 

 decreased and the globulin content increased both absolutely and 

 relatively. In mild infections and in chronic septic conditions 

 the total amount of protein present remains normal while the 

 amount of globulin and of chlorides shows a marked increase. 

 NaCl held by globulin acts as if adsorbed, i.e. exerts no osmotic 

 pressure. Globulin is precipitated by an increase in hydrogen 

 ions. It is specially sensitive to CO 2 . 



(7) Fibrinogen, a globulin. 



The osmotic pressure in the vessels is due to proteins. They 

 are also responsible for the viscosity of blood. The defibrina- 

 tion of blood lowers its viscosity to very little greater than that 

 of water. After extensive bleeding, water pours into the vessels 

 from the tissues through the lymph, and the specific gravity, 

 viscosity, etc., drop. The blood ceases to be an efficient carrier. 

 Bayliss found that the injection of a non-toxic emulsoid colloid 

 would restore normal conditions for sufficiently long a time as 

 would enable the cell-factories, especially the liver, to manu- 

 facture new blood proteins from the amino acids in the blood. 

 The most efficient sol, he found, was a solution of gum arabic in 

 Ringer's solution. The story of this discovery as told in his 

 monograph is one of the most interesting side-lights on the medico- 

 scientific work of the War. 



Clotting. 



The main use of fibrinogen lies, not in its viscosity or in its 

 osmotic pressure, but in its property of changing from a sol into 

 a gel. The clotting of plasma prevents the loss of blood and keeps 

 the blood channel free from any angularities. The evolution of 

 the knowledge of the process of clot formation has been very 

 slow and even now the physico-chemical reactions involved are 

 anything but well understood. 



Mammalian plasma, if left standing in a tube exposed to the air, 

 clots to a jelly in two to ten minutes. The gel has the same 

 volume as the sol, and no heat is evolved in the process. This 

 is a process common to most emulsoid colloids. In about half an 

 hour the clot contracts and expresses a clear straw-yellow liquid, 

 the serum. 



i.e. Plasma = Clot +Serum. 



