CHAP, i.] BLOOD. 19 



chloric acid even when diluted to far less than 1 p.c.), and it is 

 similarly soluble in dilute alkalis, but in being thus dissolved it is 

 changed in nature, and the solutions of it in dilute acid and dilute 

 alkalis give reactions quite different from those of the solution 

 of the substance in dilute neutral saline solutions. By the acid 

 it is converted into what is called acid-albumin, by the alkali 

 into alkali-albumin, both of which bodies we shall have to study 

 later on. 



3. When it is suspended in water and heated it becomes 

 altered in character, coagulated, and all its reactions are changed. 

 It is no longer soluble in dilute neutral saline solutions, not even 

 in dilute acids and alkalis ; it has become coagulated proteid, and 

 is now even less soluble than fresh fibrin. When a solution of it 

 in dilute neutral saline solution is similarly heated, a similar 

 change takes place, a precipitate falls down which on examination 

 is found to be coagulated proteid. The temperature at which 

 this change takes place is somewhere about 75 C., though shifting 

 slightly according to the quantity of saline substance present in 

 the solution. 



The above three reactions are given by a number of proteid 

 bodies forming a group called globulins, and the particular globulin \ 

 present in blood-serum, is called paraglobulin. 



One of the proteids present in blood- serum is then para- 

 globulin, characterised by its solubility in dilute neutral saline 

 solutions, its insolubility in distilled water and concentrated saline 

 solutions, its ready solubility, and at the same time conversion 

 into other bodies, in dilute acids and alkalis, and in its becoming 

 converted into coagulated proteid, and so being precipitated from 

 its solutions at 75 C. 



The amount of it present in blood-serum varies in various 

 animals, and apparently in the same animal at different times. In 

 100 parts by weight of serum there are generally present about 

 8 or 9 parts of proteids altogether, and of these some 3 or 4, more 

 or less, may be taken as paraglobulin. 



17. If the serum from which the paraglobulin has been 

 precipitated by the addition of neutral salt, and removed by fil- 

 tration, be subjected to dialysis, the salt added may be removed, 

 and a clear, somewhat diluted serum free from paraglobulin may 

 be obtained. 



This still gives abundant proteid reactions, so that the serum 

 still contains a proteid, or some proteids still more soluble than 

 the globulins, since they will remain in solution, and are not 

 precipitated, even when dialysis is continued until the serum is 

 practically freed from both the neutral salt added to it and the 

 diffusible salts previously present in the natural serum. 



When this serum is heated to 75 C. a precipitate makes its 

 appearance, the proteids still present are coagulated at this 

 temperature. 



22 



