BY DR. BURDON-SANDERSON. 177 



when it is diluted with its volume of solution ot sugar, a 

 gelatinous clot forms immediately, under ordinary tempera- 

 tures ; (3) that the process of coagulation is held in check by 

 certain neutral salts, and in particular by sulphate of soda. 

 A similar influence is exercised by sulphate of magnesia, 

 nitrate of soda, borax, and some other neutral salts. 



2. Separation of the Corpuscles from the Liquor 

 Sanguinis or Plasma in the Blood of Mammalia, by 

 Subsidence and Decantation. It is not possible to filter 

 mammalian blood in the way above described ; for the cor- 

 puscles are so small that they will run through the finest filter- 

 ing paper. We must, therefore, have recourse to subsidence. 

 The difficulties of separating the liquor sanguinis from the 

 corpuscles by subsidence depends on the length of time which 

 the corpuscles take to settle, as compared with the rapidity 

 with which the blood coagulates. In consideration of both 

 these circumstances we select 'the blood of the horse as 

 preferable to any other. In horse-blood the specific gravity 

 of the globules is 1105, that of the liquor sanguinis 1027-1028 

 (Hoppe-Seyler) : the difference is considerable, and somewhat 

 greater than in other animals. But it is of more importance 

 still that horse-blood coagulates more slowly than that of 

 other animals. 



If blood is received into one of two similar jars from a 

 bullock, into the other from a horse, it is seen that after an 

 hour or two both have coagulated firmly. In the former, the 

 clot is all of one color ; in the latter, it is divided by a tolera- 

 bly defined horizontal line into an upper colorless, and a lower 

 deeply colored, part, the upper being a little more than half 

 the depth of the other. In the one case the corpuscles have 

 had time to descend through the upper stratum of liquid before 

 it solidified, whereas in the other their descent is anticipated 

 by the coagulation of the plasma. In the horse this appear- 

 ance is alwa} r s observed when the blood taken from a blood- 

 vessel is allowed to stand. In other animals, and particularly 

 in man, it occurs only under abnormal conditions (particularly 

 inflammatory fever). It is spoken of as the "buffy coat." 



In the experiment above described, the object we have in 

 view has not been attained. The corpuscles have subsided 

 more or less completely, but the plasma no longer exists as 

 such. It has separated into clot and serum. To succeed, 

 coagulation must not only be delayed -but prevented for 

 which purpose there is but one means available, i. e., cold. At 

 the temperature of freezing, coagulation is indefinitely post- 

 poned. The blood must, therefore, as it flows from the 

 animal, be subjected to this temperature, and kept under its 

 protective influence. For this purpose a cylindrical vessel 

 made of tinplate, of the form shown in Fig. 191, is used. 

 12 



