OF THE BLOOD. 9 



plies the materials of the solids originally, and after- 

 wards their nourishment ; and from which all the other 

 fluids, with the exception of the crude (4.), are secreted 

 and derived. Of the multifarious importance of the 

 blood, we shall speak particularly hereafter. 



NOTES. 



(A) The blood is now known not to absorb any oxygen during 

 ordinary respiration. See note (C.) Sect. viii. 



(B) When blood, venous or arterial, is placed in the vacuum 

 of an air-pump* or coagulates in the air,f it emits a considerable 

 quantity of carbonic acid gas : in a paper lately read to the Royal 

 Society, but not yet printed, the quantity is said to be much 

 greater after a meal, and much less if the blood is buff}'. 



(C) Blood coagulates when cut off from communication with 

 the mass by escape from its vessels, whether warm or cold, in the 

 air or in vacuo, diluted or undiluted, at rest or in motion ; whereas 

 within the vessels, rest, which causes a cessation of intercourse 

 between the motionless portion and the general mass, is in many 

 cases sufficient to effect its coagulation. After death from a blow 

 on the stomach, lightning, arsenic, hard running, &c. it does not 

 coagulate. J 



(D) To suppose any affinity of the red particles for either the 

 lymph or the serum is erroneous. Leeuwenhoek and Hartsoeker 

 long since proved that serum merely suspends them, for if, when 

 separated, they are triturated in some serum, part of them is 

 taken up and the serum assumes a red colour 5 but if the fluid is 

 allowed to settle in a cylindrical glass, they slowly precipitate 

 themselves to the bottom, and the serum above becomes ckar, 

 as before. When blood is drawn, the serum easily separates on 

 the coagulation of the lymph. But the lymph coagulates before 



* Annales de Chimie. xiii. f Phil. Trans. 1818. p. 181. 



+ Hunter on the Blood, Sfc. 



