30 BLOOD. 



3. When it is suspended in water and heated it becomes altered in char- 

 acter, coagulated, and all its reactions are changed. It is no longer soluble 

 in dilute neutral saline solutions, not even in dilute acids and alkalies ; 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. 



One of the proteids present in blood-serum is paraglobulin, characterized 

 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 alkalies, and in its 

 becoming converted into coagulated proteid, and so being precipitated from 

 its solutions at 75 C. 



These reactions are given by a number of proteid bodies forming a group 

 called globulins, the particular globulin present in blood-serum being para- 

 globulin. 



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 our 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 filtration, be subjected to di- 

 alysis, 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 con- 

 tinued 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. 



We have some reasons for thinking that more than one proteid is present, 

 but they are all closely allied to each other, and we may for the present 

 speak of them as if they were one, and call the proteid left in serum, after 

 removal of the paraglobulin, by the name of albumin, or, to distinguish it 

 from other albumins found elsewhere, serum-albumin. Serum-albumin is 

 distinguished by being more soluble than the globulins, since it is soluble in 

 distilled water, even in the absence of all neutral salts. Like the glubulins, 

 though with much less ease, it is converted by dilute acids and dilute alkalies 

 into acid- or into alkali-albumin. The percentage amount of serum-albumin 

 in serum may be put down as 4 or 5, more or less, but it varies and some- 

 times is less abundant than paraglobulin. In some animals (snakes) it is 

 said to disappear during starvation. 



The more important characters of the three proteids which we have just 

 studied may be stated as follows : 



Soluble in distilled water and in saline solutions of all strengths . . serum-albumin. 



Insoluble in distilled water, readily soluble in dilute saline solutions, 



insoluble in concentrated saline solutions paraglobulin. 



Insoluble in distilled water, bardly soluble at all in dilute saline 

 solutions, and very little soluble in more concentrated saline solu- 

 tions fibrin. 



Besides paraglobulin and serum-albumin, serum contains a very large 

 number of substances, generally in small quantity, which, since they have 



