THE BLOOD. 49 



Thus far, then, the endeavour to prove the transformation 

 of the colourless corpuscles of the blood into tissue cells, 

 would appear to be successful ; but it is here the chain of 

 evidence breaks ;. and beyond the fact which is by no means 

 established, of their constituting epithelial cells, we have no 

 further proof to adduce of their structural incorporation with 

 the living tissues. Of this occurrence it would, of course, 

 be difficult to procure satisfactory demonstration, on account 

 of the opacity of the parts on which our examination would 

 have to be conducted. It may be remarked, however, that, 

 if founded in fact, we should expect to find a greater 

 correspondence in the size and form, &c., of the elementary 

 tissues, with that of the corpuscles from which, according 

 to some observers, those tissues are derived. * 



The corpuscular theory of nutrition, then, proposed by Mr. 

 Addison, in the present state of our knowledge can only be 

 sustained by having recourse to a certain amount of theo- 

 retical reasoning or to particular assumptions. 



The fact, however, still remains to us, that the white 

 corpuscles are concerned in nutrition, although the precise 

 manner in which they are so is still open to investigation, 

 and this fact is strengthened and confirmed by the phenomena 

 of disease. Thus, there is much evidence to show that, 

 wherever nutrition is impeded, the colourless corpuscles 

 accumulate in increased quantities in the vessels ; and it is 

 by this accumulation, also, that we are enabled to account for 

 the critical abscesses and discharges which characterise some 

 affections, and to recognise the importance which ought to 

 be attached to their occurrence. 



That the colourless corpuscles are really present in in- 

 creased numbers in the blood, in disease, is attested by the 

 evidence of numerous observers : thus, Gulliver f, Davy J, and 



* The cells of the liver and spleen resemble closely in appearance 

 the white corpuscles of the blood : between them, however, well-marked 

 differences exist, so that it is by no means to be inferred that the former 

 are derived directly from the latter. 



f Appendix to Gerber's General Anatomy, p. 20. 



j Researches, Phys. and Anat. vol. ii. p. 212. 



