156 CAPILLARY VESSELS. 
much as to be scarcely thicker than a fibre of areolar tissue 
(as inc). Branches 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 de), 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 ¢ becomes 
converted into jf, 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 
_ 
ee a 
