SERUM OF BLOOD. 87 



circular or spherical, and varying in size from the most 

 minute visible speck to the --^^ of an inch (Gulliver). 

 These molecules are very similar to those found in the 

 lymph and chyle, and are, some of them, fatty, being 

 soluble in ether, others probably albuminous, being soluble 

 in acetic acid. Generally, also, there may be detected in 

 the blood, especially during the height of digestion, very 

 minute equal-sized fatty particles, similar to those of which 

 the molecular base of chyle is constituted (Gulliver). 



The Serum. 



The serum is the liquid part of the blood remaining after 

 the coagulation of the fibrine. In the usual mode of 

 coagulation, part of the serum remains soaked in the clot, 

 and the rest, squeezed from the clot by its contraction, lies 

 around and over it. The quantity of serum that appears 

 around the clot depends partly on the total quantity in the 

 blood, but partly also on the degree to which the clot con- 

 tracts. This is affected by many circumstances : generally, 

 the faster the coagulation the less is the amount of con- 

 traction ; and, therefore, when blood coagulates quickly, it 

 will appear to contain a small proportion of serum. Hence, 

 the serum always appears deficient in blood drawn slowly 

 into a shallow vessel, abundant in inflammatory blood 

 drawn into a tall vessel. In all cases, too, it should be 

 remembered, that, since the contraction of the clot may 

 continue for thirty- six or more hours, the quantity of serum 

 in the blood cannot be even" roughly estimated till this 

 period has elapsed. 



The serum is an alkaline, slimy or viscid, yellowish fluid, 

 often presenting a slight greenish, or greyish hue, and with 

 a specific gravity of from 1025 to 1030. It is composed of 

 a mixture of various substances dissolved in about nine 

 times their weight of water. It contains, indeed, the 

 greater part of all the substances enumerated as existing 

 in the blood, with the exceptions of the fibrin and the red 



