23 THE BLOOD. 



deduction is made for the fibrin ; but, considering- its small relative quantity, any 

 possible variation ru it cannot materially affect the general conclusion. 



As regards age, Denis found the proportion of crassamentum greatest between 

 the ages of 30 and 40. Sudden loss of blood rapidly diminishes it. In two 

 women who had suffered from uterine hccmoiThage, the cras.-;ameutum amounted 

 to only 70 parts in 1000. The same effect may be observed to follow ordinary 

 venesection. In a person bled three times in one day, Lecanu found in the fii'st 

 drawn blood 139. and in the last only 76 pai-ts of crassamentum in the 1000. 

 This effect may be produced very suddenly after a bleeding. Prevo.st and Dumas 

 bled a cat from the jugular vein, and found 116 parts of crassamentum in 1000, 

 but in blood drawn five minutes afterwai-ds, it was reduced to 93. The sudden 

 loss of blood probably causes a rapid absorption of serous and watei-y fluid into 

 the vessels, and thus diminishes the relative amount of the red particles. It is 

 found that the blood of wann-blooded animals is richer in crassam.entum than 

 that of the cold-blooded ; and. among the former, the proportion is highest in 

 the class of bu-ds. 



Liquor Sanguinis, or Plasma. — The fluid part of the blood, as 

 already described, separates spontaneously into fibrin and serum. The 

 iibrin may be obtained by stirring the blood as soon as possible after it 

 is drawn, or by washing the crassamentum with water, to free it from 

 red matter. Procured in either of these ways, the fil)rin contains pale 

 corpuscles and a small proportion of fat. From dried fibrin of healthy 

 human blood, Nasse obtained nearly five per cent, of fat, and still more 

 from the fibrin of buflFy blood. The proportion of fibrin in the blood 

 does not exceed 2h parts in 1000 ; indeed, according to the greater 

 number of observers, it is not more than 2i. As a general rule, the 

 quantity is somewhat greater in arterial than in venous blood, and it 

 is increased in certain states of the body, especially in inflammatory 

 diseases and in pregnancy. 



Origin of Fibrin. — It is now ascertained that the fibrin is not 

 present, as such, in a liquid form, in the plasma, but is produced 

 at the moment of consolidation by the co-operation or combination 

 of two previously distinct substances. About thirty years ago, 

 A. Buchanan ■"■ discovered that the fluid of hydrocele, which might in 

 an unmixed state be kept for an indefinite time without coagulating, 

 very speedily congealed and separated into clot and serum when 

 mixed with a little blood. Ordinary blood-serum, blood-clot, especially 

 washed clot, and buffy coat, even after being dried and long kept, 

 when added in small proportion to the hydrocele-fluid, produced the 

 same etfect. From these facts Buchanan concluded that fibrin exists 

 as a liquid both in hydrocele-fluid and in the liquor sanguinis, that 

 liquid fibrin does not coagulate spontaneously, but requires for that 

 end the influence of some " suitable reagents," that such a reagent is 

 naturally present in the blood, and brings about the solidification of its 

 fibrin in the natural process of coagulation, and that it is absent from 

 the hydrocele-fluid, but when supplied by tlie addition of blood, causes 

 the fluid filH-in to solidify. On further reasoning on the facts he had 

 observed, Dr. Buchanan was led to beheve that "coagulant power" 



* Proceedings of the Glasgow PhilosopLicul Society, 1845. 



