84 PHYSIOLOGICAL CHEMISTRY. 



globulin, which is possibly identical with serum globulin. This 

 substance has been obtained from different organs, from the 

 liver, from the pancreas, from muscle plasma, etc. Some 

 of the globulins described as cell globulins have a lower coag- 

 ulating temperature than the true serum globulin. 



In the crystalline lens of the eye a body has been long known 

 which is called crystallin. In coagulation temperature and 

 specific rotation this crystallin appears distinct from serum 

 globulin, and further, it seems to be made up of two related 

 substances, a and ft crystallins. 



Globulins have been described in milk and egg and also 

 in the vegetable kingdom under the name of phytoglobulins or 

 phytovitellins. This last designation indicates that they may 

 be classed under the head of the nucleo-albumins, with which 

 bodies they have much in common. In this connection some- 

 thing will be said about them later. 



COAGULATING PROTEINS. 



Several extremely important substances belong in this group, 

 which, like fibrinogen, have the property of spontaneous coagu- 

 lation. In nature they exist normally in the soluble and dis- 

 solved form, from which, under certain influences, not always 

 well understood, they pass to the solidified condition. This 

 coagulation is a different thing from that produced by heat- 

 ing to a high temperature or by the addition of reagents; 

 the changes in the latter case seem to be more profound. We 

 use in English the term coagulation to describe both classes of 

 alterations, which are really of a very different character, as 

 will appear from what follows. 



FIBRINOGEN. Blood contains a peculiar protein body in 

 small amount, to which it owes its property of spontaneous 

 coagulation. This body is called fibrinogen and the product 

 of coagulation is known as -fibrin. The nature of and impor- 

 tant factors in this change have been long subjects of investi- 

 gation and discussion; it can not be said that the matter has 

 been fully explained in all its bearings. The essential points 



