COAGULATION. 453 



Other Proteins of the Blood-serum or Blood-plasma. From time to time 

 other protein bodies have been described in the serum or plasma of the blood. 

 In the serum after coagulation Hammarsten has obtained a globulin body, 

 fibrin-globulin, which he supposes may be split off from the fibrinogen dur- 

 ing the act of clotting. Faust describes an albuminoid substance, glutelin, 

 which is present in the blood and is usually precipitated together with the 

 paraglobulin. A number of observers have noted the existence in blood 

 of a protein not coagulated by heat. By some authors this has been de- 

 scribed as a peptone or an albumose (Langstein), by others as an ovomucoid 

 (Zanetti), and by others still (Chabrie) as a peculiar protein for which the 

 name albumon has been proposed. By others still, this non-coagulable pro- 

 tein obtained from serum or plasma has been explained as an artificial 

 product arising from the globulins of the blood during the process of remov- 

 ing the coagulable proteins by heating. So, too, nucleoprotein substances 

 have been described in the blood-serum by several observers, most recently by 

 Freund and Joachim. It is quite possible, however, that the substance de- 

 scribed as nucleoprotein is in reality a mixture or combination of lecithin and 

 protein. Most of the protein when precipitated from the blood carries down 

 with it some lecithin, and will therefore show a reaction for phosphorus. It 

 can be shown that the phosphorus present is, in most cases at least, remov- 

 able by boiling with alcohol, and there is at present no entirely satisfactory 

 proof that nucleoprotein exists in the blood. 



Coagulation of Blood. One of the most striking properties of 

 blood is its power of clotting or coagulating shortly after it escapes 

 from the blood-vessels. The general changes in the blood during 

 this process are easily followed. At first perfectly fluid, in a few 

 minutes it becomes viscous and then sets into a soft jelly which 

 quickly becomes firmer, so that the vessel containing it may be 

 inverted without spilling the blood. The clot continues to grow 

 more compact and gradually shrinks in volume, pressing out a 

 smaller or larger quantity of a clear, faintly yellow liquid to which 

 the name blood-serum is given. The essential part of the clot is the 

 fibrin. Fibrin is an insoluble protein not found in normal blood. 

 In shed blood, and under certain conditions in blood while still in the 

 blood-vessels, this fibrin is formed from the soluble fibrinogen. 

 The deposition of the fibrin is peculiar. As seen in ordinary 

 microscopical preparations, the fibrin forms very delicate threads 

 which are united to make a fine reticulum. When the process is 

 observed with the aid of the ultramicroscope it can be seen that 

 the fibrin is deposited in the form of very fine needles, which have 

 the appearance of acicular crystals.* When the process of clot- 

 ting is very slow the needles may remain separate for a long time 

 until their number is greatly increased, but in normal clotting the 

 process, once it has started, is completed quite rapidly, the final 

 result being a dense network or meshwork of the fibrin needles 

 (Fig. 186). This form of precipitation of a colloid solution, or 

 the formation of a hydrogel from a hydrosol, is unique so far as 

 our knowledge goes. Solutions of fibrinogen may be precipitated, 



* See Stiibel, "Pfluger's Archiv f. d. ges. Physiologic," 156, 361, 1914; and 

 HoweU, "American Journal of Physiology," 35, 143, 1914. 



