156 CAPILLARY VESSELS. 



much as to be scarcely thicker than a fibre of areolar tissue 

 (as in c). Brauches are also sometimes given off from these 

 wider parts, which likewise diminish very rapidly to the same 

 degree of minuteness, without reaching another dilated part 

 (as at d e), and which are, therefore, blind ones. According 

 to the above view of the development of the capillaries, these 

 appearances may be explained in the following manner : the 

 wider portions, a, b, &c, are the bodies of the primary cells. 

 Hollow processes, as at d, are sent out from the bodies of the 

 cells as the result of a more vigorous growth in different situ- 

 ations, precisely as is the case in all stellate cells. These 

 prolongations meet with similar ones from other cells, and thus 

 produce the form c. But being hollow, they are capable of 

 expansion during their growth, and thus the canal c becomes 

 converted into /, and at length into g, which is as wide as an 

 ordinary capillary vessel. A more accurate analysis of the 

 observations, however, is necessary to enable us to judge of 

 the correctness of this explanation. It might be doubted, in 

 the first place, whether these were really capillaries. The blood 

 flows uninterruptedly through the ordinary capillaries, but there 

 are no blood-corpuscles in these canals, at least in the more 

 minute ones ; they are, therefore, more difficult to discover, 

 and readily give rise to a doubt whether they are canals. 

 But their direct continuity with the ordinary capillaries may be 

 clearly demonstrated, and blood-corpuscles actually enter the 

 wider ones. If they be true capillary vessels, they may either 

 be ordinary ones in a state of contraction, or they must repre- 

 sent a certain stage of their development. But if it be difficult 

 to conceive that a capillary vessel can have the power to con- 

 tract itself almost to the minuteness of a filament of areolar 

 tissue, such an assumption cannot be supported at all in 

 respect to the blind branches, which do not join any other 

 vessel, as at d, This form might, indeed, be admitted to be a 

 certain stage of development, although not of the kind de- 

 scribed above ; but branches might be sent off from the 

 capillaries already existing, which again might give off others. 

 The objection, that such an explanation does not account for 

 the varying width of these capillaries, might be met by as- 

 suming that circumstance to depend upon the surrounding 

 substance. It is, therefore, necessary to see the primary cells 



