72 THE BLOOD. 



that before appeared to form the whole corpuscle, remains 

 attached as the nucleus of the cell (Fig. 29). 



A remarkable property of the white corpuscles, first observed 

 by Mr. Wharton Jones, consists in their capability of assuming 

 different forms, irrespective of any external influence. If a 

 drop of blood be examined with a high microscope power 

 under conditions by which loss of moisture is prevented, at 

 the same time that the temperature is maintained at about the 

 degree natural to the blood as it circulates in the living body, 

 the leucocytes can be seen alternately contracting and dilating 

 very slowly at various parts of their circumference shooting 

 out irregular processes, and again withdrawing them partially 

 or completely, and thus in succession assuming various irreg- 

 ular forms. 



These movements, called amoeboid, from their resemblance to 

 the movements exhibited by an animal called the Amoeba, the 

 structure of which is as simple as that of a white blood-cor- 

 puscle, are characteristic of the living leucocyte, and form a 

 good example of the contractile property of protoplasm, before 

 referred to. Indeed, the unchanging rounded form which the 

 corpuscles present in specimens of blood examined in the 

 ordinary manner under the microscope, must be looked upon 

 as the shape natural to a dead corpuscle, or one whose vitality 

 is dormant, rather than as the proper shape of one living and 

 active. 



Besides the red and white corpuscles, the microscope reveals 

 numerous minute molecules or granules in the blood, circular 

 or spherical, and varying in size from the most minute visible 

 speck to the -g^ 1 ^ 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 prob- 

 ably 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 con- 

 stituted (Gulliver). 



The Serum. 



The serum is the liquid part of the blood remaining after 

 the coagulation of the fibrin. In the usual mode of coagula- 

 tion, 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 "de- 

 pends partly on the total quantity in the blood, but partly 

 also on the degree to which the clot contracts. This is affected 

 by many circumstances : generally, the faster the coagulation 



