THE BLOOD. 63 



the blood-vessels and the tissues lying external and adjacent 

 to them, is doubtless established, through the operation of the 

 principle of exosmosis, whereby a slow exudation of the fluid 

 fibrin of the blood is perpetually going forward. Now it is 

 the opinion of most of the German physiologists, and it is 

 the view best supported by facts, that this fluid fibrin is to 

 be regarded as the true blastema, out of which all the dif- 

 ferent elementary tissues and structures of the body proceed, 

 and this not by any power inherent in itself, it being, as 

 respects the final form which it is made to assume, totally 

 inert and indifferent, and which form is impressed upon it by 

 a vis insita, or peculiar power and faculty belonging to each 

 organ and structure of the animal fabric. 



While the fibrin circulates in the blood it retains its fluid 

 form ; soon after the cessation of the circulation, and whether 

 within or without the system, it passes from the fluid state 

 to the condition of a solid: now, on the principle of endosmosis, 

 which has to be so often referred to in the explanation of 

 numerous phenomena, in the solidifying power of the fibrin, 

 and in the vis insita of the different tissues, we recognise the 

 chief and fundamental causes which regulate nutrition, 

 growth, and secretion. 



It would thus appear that the globules of the blood (the 

 red globules are more particularly alluded to) are not to be 

 regarded as either cytoblasts or primary cells, forming by 

 direct apposition the solids of the body, and that therefore 

 they do not express the last degree of elaboration of which 

 the fibrin of the blood is susceptible. 



Again, then, we have to ask ourselves the question, what 

 is the end, or final condition, of the red blood globules ? Direct 

 observation is wanting to aid us in the solution of this difficult 

 inquiry, which, however, admits of an indirect reply being 

 given : we have seen that no means of egress from the blood- 

 vessels is, under ordinary circumstances, permitted to the red 

 blood globules, and therefore we are driven to the conclusion 

 that, having performed the important function to which we 

 have already alluded, viz. that of carriers of oxygen from the 

 lungs throughout the system, and of carbon from the latter 



