CHAPTER VI. 



OF THE SERUM OF THE BLOOD, AND PARTICULARLY OF THE 

 MILK-LIKE SERUM. 



THE serum, when separated from the crassamentum, by let- 

 ting the blood rest in the basin into which it is received, is a 

 fluid, apparently homogeneous and transparent, of a yellowish 

 colour, saltish to the taste, in consistence thicker than water, 

 and its specific gravity, according to Dr. Jurin, is to water as 

 1030 to 1000 (LII). 



When chemically examined the serum is found to consist of 

 a mucilaginous substance, which is dissolved in a water that 

 contains a small quantity of neutral salts. The mucilaginous 

 substance of the serum agrees with the coagulable lymph of 

 the blood in being fixed or coagulated by heat ; but the degree 

 necessary for the coagulation of the serum is greater than 

 that which is necessary for fixing the lymph, for the lymph is 

 coagulated by a heat between 114 and 120J degrees of Fahren- 

 heit's thermometer (see Experiment 9th) ; whilst the serum 

 requires 160 to coagulate it (LIII) : (see Experiment 10th). 



(LII.) Dr. Jurin's estimate* is probably rather above the mean. In 

 five trials, Dr. Marcet b found the specific gravity of serum of human 

 blood from 1024-5 to 1032'5. Serum of the blood of different animals, 

 Dr. Davy c found to vary between 1020 and 1031 ; and of man labouring 

 under disease, from 1021 to 1033. In soldiers bled for slight ailments, 

 I have seen the serum 1025, 1026, 1028, 1029, and 1031; in all these 

 instances the blood had a healthy appearance. The specific gravity of the 

 serum of buffy blood is mentioned in Note xxii. The following num- 

 bers show the mean of Dr. Davy's observations on the sp. gr. of the 

 blood and of the serum of mammalia : 



Arterial blood . 1050 Venous blood . 1053 



Arterial serum . 1022 Venous serum . 1026 



(LIII.) On the heat most favorable to the coagulation of fibrin, see 

 Notes in and xvi ; and on the coagulation by heat of serum, Note xvu. 



a Phil. Trans. 1719, xxxvi, 1007. c Researches, Physiol. and Anat. ii, pp. 



b Med. Chir. Trans. 1813, ii, 366. 17-25, 34-39. 



