CHAP. II.] THE BLOOD. 27 



blood colouring matter does not diffuse out of the blood corpuscles into 

 solutions of common salt of considerable strength. Litmus paper is 

 moistened with a strong solution of salt and a drop of the blood to be 

 tested is placed upon it ; after a few seconds a drop of the same salt 

 solution is placed over the drop of blood ; the liquid is then sucked up by 

 means of filter paper. By following this method the blood can be so 

 removed from the test-paper that the colour of the latter may be readily 

 observed. The litmus paper to be used for this purpose must be highly 

 glazed and the tincture of litmus used in its preparation must have been 

 neutralized with acid until its colour is violet. 



By adding standard solutions of acids to blood, and employing the 

 above method for ascertaining when the reaction became faintly acid, 

 Zuntz determined the previously mentioned diminution of alkalinity 

 of blood removed from the body. 



The Pheno- As it circulates in the blood-vessels of the living body, 



agnation C ~ tne blood consists, as we have said, of a liquid, the so- 

 called liquor s. plasma sanguinis (often designated 

 blood-plasma, or more shortly the plasma), holding in suspension the 

 blood corpuscles. Within a short time of its being shed usually 

 between two and six minutes the process known as coagulation 

 commences a process in which the blood passes first into the state 

 of a soft red jelly, which gradually acquires greater consistence, 

 and which, by a contraction of one of its constituents, expresses a 

 fluid the serum, which surrounds the clot, and in which the latter 

 often ultimately floats. 



If we desired to ascertain the exact time when this coagulation 

 commenced in a sample of blood, we should collect it in a watch-glass 

 and at very short intervals pass a needle through the liquid ; as soon 

 as coagulation had set in the needle would, in its passage through 

 the fluid, entangle itself in the newly formed jelly, which would then 

 be apparent on drawing the needle out. 



When blood coagulates, the process usually commences on the 

 surface of the liquid and then near the sides of the vessel which 

 contains it, the newly formed coagulum having in the former case the 

 appearance of a pellicle. Very rapidly, however, the process invades 

 the whole mass of the blood, which then presents the appearance of a 

 soft, easily broken, jelly. Soon this acquires greater consistence, so 

 that the blood has, as it were, taken a cast of the vessel which 

 contained it, adhering closely to its sides and permitting of the vessel 

 being inverted without any escape of the contents; at the same time 

 drops of serum begin to transude from the clot. This transudation 

 of serum is brought about by the contraction of the clot and continues 

 for a time varying between ten and forty-eight hours, at the end of 

 which the clot is found to be surrounded by serum. According to 

 Nasse, the first stage of coagulation (characterized by the formation 

 of a pellicle) commences in the blood of men in about 3 minutes 

 45 seconds, in that of women in 2 minutes 50 seconds; the second 

 stage, in which not only the surface but the portions of blood next to 



