78 THE BLOOD. 



cocytes can be seen alternately contracting and dilating 

 very slowly at various parts of their circumference, shoot- 

 ing out irregular processes, and again withdrawing them 

 partially or completely, and thus in succession assuming 

 various irregular forms. 



These movements, called amoeboid, from their resem- 

 blance to the movements exhibited by an animal called 

 the Amoeba, the structure of which is as simple as that of 

 a white blood-corpuscle, are characteristic of the living 

 leucocyte, and form a good example of the contractile pro- 

 perty of protoplasm, before referred to. Indeed, the unchang- 

 ing rounded form which the corpuscles present in specimens 

 of blood examined in the ordinary manner under the micro- 

 scope, 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 - B J u 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 fibrin. 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- 



