CHAP. II.] THE BLOOD. 33 



above proportions (Hewson's method 1 ), it is more usual to mix the 

 blood with a saturated solution of the salt; the blood is received 

 directly into a vessel, which contains }th of its volume of a saturated 

 solution of sodium sulphate 2 , and the two liquids are gently mixed. 



b. Magnesium sulphate, as has been shewn by Schmidt 3 , 

 Semmer 4 and by Hammarsten, is decidedly preferable to sodium 

 sulphate for hindering the coagulation of the blood and for yielding 

 a plasma suitable for experimental researches on the formation of 

 fibrin. According to Semmer four parts of blood are mixed with 

 one part of a solution of magnesium sulphate containing 25 p. c. of 

 the salt. According to Hammarsten 5 the blood is mixed in the 

 same proportion with a saturated solution of magnesium sulphate 6 . 



In addition to the substances, which, when added in suitable 

 proportions, prevent the coagulation of the blood, there are others 

 which merely postpone its occurrence and facilitate the separation 

 of blood corpuscles from the plasma. Thus when frog's blood is 

 mixed with its own volume of a ^p.c. solution of cane-sugar, the 

 corpuscles may be separated from it by filtration, and there passes 

 through the filter-paper a clear fluid which consists of plasma 

 diluted with solution of sugar, which coagulates after a short 

 interval. This method of separating the blood corpuscles from the 

 plasma was suggested by Johannes Muller 7 . 



In relation to the action of neutral salts in hindering the coagula- 

 tion of the plasma it must be remembered that these substances 

 only exert their action when present in certain proportions ; if added 

 in too small quantities to blood, coagulation occurs, and if sufficient 

 water be added to blood or plasma which has been kept from 

 coagulating, the process sets in. Thus, as Hewson shewed, if to blood 

 which has been maintained in a fluid state by the addition of solid 

 sodium sulphate in the proportions previously mentioned, there be 

 added twice its volume of water, in a short time the whole will 

 coagulate. 



Properties Plasma, obtained by subjecting blood to a low 



temperature, is a viscous liquid possessing the same 

 colour as the serum which separates from the blood 

 of the same animal after coagulation ; if kept at a temperature below 

 5 C. it may be filtered from any colourless corpuscles floating in it 8 . 



Hewson's Works, p. 11. 

 Denis, Memoire sur I'e sang, 1859, p. 31. 

 A. Schmidt, Haematologische Studien. Dorpat, 1865, p. 44. 

 Semmer, quoted by Gscheidlen, Physiologische Methodik, p. 342. 

 Hammarsten, "Zur Lehre von der Faserstoffgerinnung," Pfliiger's Archiv, Vol. 

 xiv. (1877) p. 220. 



6 Many other neutral salts may be employed instead of those previously mentioned, 

 as was shewn by Hewson, Gulliver and Davy. The reader will find much valuable 

 information on this subject in Gulliver's edition of Hewson's Works, p. 12, and in 

 Davy's Researches, Vol. n., p. 101. 



7 Joh. Muller, "Beobachtungen,zur Analyse der Lymphe, des Blutes und des Chylus." 

 Poggendorff 's Annalen, Vol. xxv. (1832) p. 540. 



' Alex. Schmidt, Pfliiger's Archiv, Vol. xi. (1875) p. 318. 



G. 3 



