CHAP. II.] THE BLOOD. 43 



fact that the blood retains its fluidity within the healthy and yet 

 living blood-vessels even though the circulation have ceased; the 

 second is disproved by the fact that blood retained in vessels which 

 contain no air and are shut off from air, coagulates with readiness ; 

 the third is summarily and conclusively disproved by the facts that 

 whilst a low temperature hinders coagulation instead of hastening 

 it, a temperature such as that of the body of warm-blooded animals 

 is specially favourable to its occurrence. The fourth view is set 

 aside by the fact that the coagulation of the blood can be post- 

 poned almost indefinitely by exposure to a sufficiently low tem- 

 perature or by the addition to it of certain salts, and that after long 

 periods have passed, the experimenter may, by altering the con- 

 ditions, induce the previously inhibited coagulation, as for instance 

 by suitably diluting blood of which the coagulation has been 

 prevented by the addition of large quantities of neutral salts. 



If coagulation were a vital act, the results of the above experi- 

 ments would, as Gulliver remarked 1 , be equivalent to a demonstra- 

 tion that we can pickle the life of the blood, that it is preserved 

 after repeated freezing and thawing, and that the blood may remain 

 alive many hours after the death of the body, when the muscular 

 fibre has lost its irritability, the limbs have stiffened, and even 

 partial decomposition has begun. 



In considering the progress of research and the succession of 

 doctrines relating to coagulation, it is well to remember that the 

 following facts amongst many others were demonstrated by Hewson, 

 and were published by him in the year 1772 : Firstly, that the coagu- 

 lation of the blood is due to the coagulation of the liquor sanguinis, 

 a fact which he proved (a) by skimming off the liquor sanguinis 

 of the slowly coagulating blood of inflammatory diseases after 

 the corpuscles had subsided, and determining that it coagulated, 

 (6) by ligaturing a vein so as to include fluid blood within it, and 

 opening it after the corpuscles had subsided, and drawing off the clear 

 liquor sanguinis, which then coagulated. Secondly, that the coagula- 

 tion of the blood drawn from the body cannot be explained as due to 

 loss of heat, to arrest of motion, or exposure to air. Thirdly, that 

 coagulation may be restrained by cold and by the addition of neutral 

 salts to blood, the process setting in when the conditions are 

 modified. Fourthly, that the walls of the living blood-vessels exert 

 a remarkable influence in restraining coagulation. 



Discoveries The serous sacs of the body, even in health, contain 



of Buchanan. small quant i t i e s of liquid which at first sight appears 

 closely to resemble the serum of blood, but which is similar to that 

 found in the lymphatic vessels, viz. lymph. Of such serous sacs the 

 pericardium is the one which invariably contains after death more or 

 less liquid, which has received the name of liquor pericardii. In 

 disease, the fluid contents of the serous sacs may however increase 



1 Hewson's Works, note 12, p. 21. 



