44 PROPERTIES OF 



was later in coagulating than that in the last, and since the 

 blood in the first cups alone had a size, is it not probable, that 

 even during the short time taken up in the evacuation, the pro- 

 perties of the lymph had been changed, and that it was owing 

 to this change (xxiv) that the size disappeared ? It might in- 

 deed, at first sight, seem possible that the bleeding had only 

 let out the vitiated part ; but this is not at all likely ; for, sup- 

 pose a part only of the blood was vitiated, that part must have 

 been equally diffused through the whole mass, and there is no 

 probability of its getting out of the vessels before the rest of 

 the blood; and consequently it ought to have appeared in the 

 last equally as in the first cup, but it did not. Bleeding, there- 

 fore, in those cases alters the nature of the blood, not by re- 

 moving the vitiated part, and giving room for new blood to be 

 formed, as has been supposed ; but probably by changing that 

 state of the blood-vessels, on which the thinness, and lessened 



(xxiv.) The change probably consists in a dilution of the blood, as 

 it may be supposed that the contents of the lymphatic vessels are rapidly 

 poured into the veins as the blood flows out. The evidence originally 

 given by Dr. Davy in his Thesis, a that the blood which flows last and 

 coagulates first contains most water, is mentioned in Note i. I did not 

 observe, in some experiments, that adding distilled water to the blood 

 hastened its coagulation, though it was hastened by the addition of 

 serum, and still more by the addition of red corpuscles : See Exp. 45-63, 

 'Edin. Med. and Surg. Journ.' vol. 64, p. 373. Mr. Prater, b Schrceder 

 Van der Kolk, and Dr. Alison, had before observed the same effect 

 from diluting the blood with serum, and applied it to account for the 

 more rapid coagulation of the last flowing blood. 



On the curious subject of the change in the properties of the blood 

 during its evacuation, there are the three following hypotheses : 1 . That 

 of Quesnay d and Hewson, in which vascular action is supposed to be 

 the chief cause. 2. That of Dr. Davy, e in which the change is con- 

 jectured to be owing to blood from different parts of the body entering 

 the stream flowing in any bloodletting. 3. That of Liebig, described 

 in Note xvin, that albumen and fibrin are isomerical substances. The 

 second hypothesis is not incompatible with the third. Mr. Thackrah f 

 has given an account of the difference in the blood from divers vessels. 

 But some of his results are so extraordinary as to require further ex- 

 amination ; the wide range, for instance, in the specific gravity of blood 

 and its serum from the portal vein. 



a Tent. Exp. quaedam de Sang. comp. d Traite de la Saignee, p. 415, nouv. ed. 



p. 37, 8vo, Edin. 1814. 8vo, Paris, 1750. He refers only to 



b Exp. Inq. in Chem. Physiol.- p. 105, the excess of fibrin in the blood in 



8vo, Lond. 1832. inflammation. 



c Outlines of Physiology and Path., p. e Researches, ii, 67, 83. 



46, 8vo, Edin. 1833. f On the Blood, ed. 1834, p. 94 et seq. 



