Develojp merit, <&c., of Blood-vessels. By G. and F. E. Hoggan. 581 



The thinning or withering of the wall which we have referred 

 to, is evidently a process of absorption of the excess of protoplasm 

 which the cell had accumulated after it had taken its position as a 

 part of the capillary wall at its first development During this 

 absorption, moreover, particles of a peculiar fatty-like substance 

 show themselves, as at e. Fig. 19, on the absorbing protoplasm, 

 which refuse to stain with colouring reagents ; but when logwood 

 has been used it appears of a yellowish-brown colour, in strong 

 contradistinction with the blue or purple tint of the healthy nuclei 

 or protoplasm. 



More peculiar still is the relation which the intercepted 

 portions of capillary bear to the blood-corpuscles, numbers of which 

 in many cases become shut up in such intercepted portions, as in 

 Figs. 17 and 19. For the purpose of studying tlie changes under- 

 gone by those blood-corpuscles, we especially recommend the 

 pyrogallate of iron staining process, for while the nuclei and pro- 

 toplasm of the healthy elements are very well shown by it, the 

 blood-corpuscles seem to have a special affinity for the colouring 

 matter and stain intensely black, so that there is no difficulty ia 

 watching their behaviour until they have become completely ab- 

 sorbed. This faculty of staining intensely is probably due to the 

 great amount of iron which they normally contain, but whatever 

 the cause may be, the fact is very evident. The change which 

 takes place in these elements can be easily followed, even if it 

 cannot be explained. The corpuscles enclosed in a portion of 

 capillary undergoing the thinning or absorbing of its protoplasm, 

 are seen to become paler and transparent, as at h, Fig. 11), and 

 smaller in size, until a point is reached when they can no longer 

 be detected, as if they had dissolved away within the absorbing 

 protoplasm of the capillary cell, and no vestige of them remained 

 behind. It is highly probable that the yellowish fat-particles, c c, 

 Fig. 19, already alluded to, are really composed of a modification of 

 the blood pigment from the corpuscles, a point we have not the 

 necessary instruments to determine. 



This reference to blood-corpuscles within intercepted portions 

 of capillary, leads us to the much debated question of the presence 

 of blood-corpuscles within cells already referred to, and of the 

 signification of those appearances in what have been named vaso- 

 formative cells by Professor Kanvier, with regard to which we have 

 also given Dr. Thin's opinion that they are merely spaces in the 

 omentum to which the term cell is not apjilicable. This question 

 also brings us to the consideration of the retrogression of blood- 

 vessels })hysiologically in connection with the development of an 

 animal. Professors Kanvier and Schutfer independently announced 

 the discovery of cells containing blood- corpuscles, the one having 

 Ibund them in the skin of embryo rats, ana the other in the serous 



