BLOOD. 351 



precipitated by saturation with common salt (NaCl). In neutral or feebly acid 

 solutions it coagulates upon heating to 75 C. Hammarsten gives its element- 

 ary composition as 



c H N s o 



52.71 7.01 15.85 1.11 23.24 



These figures must also be received as approximate, as it is not absolutely cer- 

 tain that the substance analyzed was chemically pure. Paraglobulin occurs in 

 blood, in lymph, and in the normal and pathological exudations. The amount 

 of paraglobulin present in blood varies in different animals. Among the mam- 

 malia the amount ranges from 1.78 per cent, in rabbits to 4.56 per cent, in the 

 horse. In human blood it is given at 3.10 per cent., being less in amount, 

 therefore, than the serum-albumin. It will be seen, upon examining the 

 tables of composition of the blood-plasma and blood-serum of the horse 

 (p. 349), that more of this proteid is found in the serum than in the plasma. 

 This result, which is usually considered as being true, is explained by supposing 

 that during coagulation some of the leucocytes disintegrate and part of their 

 substance passes into solution as a globulin identical with or closely resembling 

 paraglobulin. The figures given above show that a considerable amount of 

 paraglobulin is normally present in blood. It is reasonable to suppose that, 

 like serum-albumin, this proteid is valuable as a source of nitrogenous food 

 to the tissues. It is uncertain, however, whether it is used by the tissues 

 directly as paraglobulin or is first converted into some other form of proteid. 

 It is entirely unknown, also, whether its value as a proteid supply is in any 

 way different from that of serum-albumin. The origin of paraglobulin 

 remains undetermined. It may arise from the digested proteids absorbed 

 from the alimentary canal, but there is no evidence to support such a view. 

 Another suggestion is that it comes from the disintegration of the leucocytes 

 (and other formed elements) of the blood. These bodies are known to contain 

 a small quantity of a globulin resembling paraglobulin, and it is possible that 

 this globulin may be liberated after the dissolution of the leucocytes in the 

 plasma, and thus go to make up the normal supply of paraglobulin. This 

 suggestion, however, is theoretical. The fact remains that at ^present the 

 origin and the special use of the paraglobulin are entirely unknown. 



Fibrinogen is a proteid belonging to the globulin class and exhibiting all 

 the general reactions of this group. It is distinguished from paraglobulin by 

 a number of special reactions ; for example, its temperature of heat coagula- 

 tion is much lower (56 to 60 C.), and it is completely thrown down from its 

 solutions by saturation with NaCl as well as with MgSO 4 . Its most import- 

 ant and distinctive reaction is, however, that under proper conditions it gives 

 rise to an insoluble proteid, fibrin, whose formation is the essential phenom- 

 enon in the coagulation of blood. Fibrinogen has an elementary composition, 

 according to Hammarsten, of 



c H N s o 



52.93 6.90 16.66 1.25 22.26 



Fibrinogen is found in blood-plasma, in lymph, and in some cases, though not 



