CHAP, i.] BLOOD. 25 



foregoing section is probably undergoing changes from the moment 

 of being shed, are very great; our information concerning the 

 composition of the serum and of the corpuscles is much more trust- 

 worthy. 



Composition of serum. In 100 parts of serum there are in 

 round numbers 



Water 90 parts 



Proteid Substances 8 to 9 



Fats, Extractives 1 , and Saline Matters 2 to 1 

 The proteid substances present in serum are 2 : (1) The so-called 

 $erum albumin, (2) parafflobulin. The paraglobulin, as has been 

 stated in the preceding section, may be removed from the serum in 

 several ways: viz. by passing carbonic acid through, or by cautiously 

 adding dilute acetic acid to, the diluted serum, or more completely 

 by saturating the undiluted serum with magnesium sulphate. 

 When the whole of the paraglobulin has been removed a con- 

 siderable quantity of proteid material is still left in the serum 

 in the form known as serum albumin, distinguished from, 

 paraglobulin among other characters by its being soluble in 

 distilled water, and therefore not requiring for its solution the 

 presence of a neutral salt 3 . From the researches of Hammar- 

 sten it would appear that, owing to imperfect methods the 

 amount of paraglobulin in serum has been much underrated. 

 According to him, the quantity though varying in different animals, 

 is at times equal to and sometimes even greater than that of the 

 serum albumin. Even if we were to accept as definitely proved 

 the view that paraglobulin in some form or other is in some 

 way associated with the formation of fibrin, it seems hardly 

 probable that the whole of this large quantity of paraglobulin 

 present in serum is fibrinoplastic, i.e. capable of taking part in 

 the formation of fibrin. We cannot at present however attach 

 any definite functions to the paraglobulin and serum albumin 

 respectively, nor do we know much as to what extent they vary 

 in quantity, though the interesting observation has been made 

 that in snakes the serum albumin disappears during starvation, 

 while the paraglobulin is fairly constant. When serum, after the 

 cautious addition of acetic acid in order to neutralize its alkalinity, 

 is heated to about 75 C. both the serum albumin and paraglobulin 

 are thrown down in the form known as coagulated proteids, sub- 

 stauces characterized by their great insolubility. This 'coagulation' 

 by heat of these and other proteids is, it perhaps need hardly be 

 repeated, not to be confounded with the coagulation of plasma due 

 to the appearance of fibrin. 



1 This word is used to denote substances of varied origin and nature, occurring 

 in small quantities, and therefore requiring to be ' extracted ' by special means. 



a There seems no longer any reason to distinguish a serum-casein from paraglo- 

 bulin, see Appendix. 



3 For further details see Appendix. 



