THE BLOOD. 31 



Some observers have compared it to a vesicle. This defini- 

 tion does not seem to be altogether satisfactory ; for although 

 each corpuscle possesses the endosmotic properties common to 

 a vesicle, no membrane, apart from the general substance of 

 the globule, (I speak more particularly of the human blood 

 disc,) has been demonstrated as belonging to it, 



Each globule in man may therefore be defined to be an 

 organism of a definite form and homogeneous structure, 

 composed chiefly of the proteine compound globuline, which 

 resembles albumen very closely in its properties; its sub- 

 stance externally being more dense than internally, it being 

 endowed with great plastic properties, and, finally, being the 

 seat of the colouring matter of the blood. 



The extent to which the red globule is capable of 

 altering its form, is truly remarkable. If it be observed 

 during circulation, it will be seen to undergo an endless va- 

 riety of shapes, by which it accommodates itself to the space 

 through which it has to traverse, and to the pressure of the 

 surrounding globules. The form thus impressed upon it is not 

 however permanent, for as soon as the pressure is removed, it 

 again instantaneously resumes its normal proportions. On 

 the field of the microscope, however, the corpuscles may be so 

 far put out of form, as to be incapable of restoration to their 

 original shape. 



Some observers have assigned to the red globule a com- 

 pound cellular structure, comparing it to a mulberry. It 

 need scarcely be said that such a structure does not really 

 belong to it. A puckered or irregular outline is not un- 

 frequently presented by many globules : this is due sometimes 

 to evaporation, and then arises from the presence around the 

 margin of the disc, and occasionally over the whole surface, 

 of minute bubbles of air*; and at other times it is the result of 

 commencing decomposition, or the application of some special 

 re-a^ent, as a solution of salt, in which cases a true change 

 in the form, but not in the structure of the globule, does 



* This vesiculated appearance of the blocxTcorpuscles may be produced 

 at once by pressure. 



