568 Transactions of the Societtj. 



XVIII. — On the Development and Betrogression of Blood-vessels. 



By George Hoggan, M.B., and Frances Elizabeth Hoggan, 



M.D. 



I^Rectd Uth April, 1880.) 

 Plate XV. 



At the present day it is not necessary to hold pessimist ideas in 

 histology in order to admit that our knowledge of the manner in 

 which blood-vessels are formed is still unsatisfactory; and. although 

 for the last thirty years the most eminent histologists have sought 

 to elucidate the question, it may fairly be said that the very latest 

 opinions enunciated, differing as they do from all previous ones, are 

 in no way more satisfactory. Although many of these opinions 

 appear diametrically opposed to each other, they are principally so, 

 it seems to us, in being too exclusive in their application; and 

 with the view of reconciling them, we desire to put on record a 

 series of clearly ascertained facts or appearances which certain new 

 histological processes devised by ourselves have enabled us to obtain. 

 In our opinion, the general disagreement among histologists 

 upon this question is caused, in the first place, by the unsuitability 

 of the tissues in which it has been studied, and in the second place, 

 by the mode of preparation employed. Paradoxical though it may 

 appear, we have learnt from experience that the worst place in 

 which to study the development of any special tissue is the em- 

 bryo itself. There the embryonic cells are so little differentiated 

 from each other in shape, the intercellular substance or matrix is 

 so extremely scanty, while the process of developmental growth is 

 so rapid, that it is almost impossible to obtain a clear demonstra- 

 tion. The membranous expansion of the tail of a living tadpole, 

 which has been so often employed for this kind of research, and from 

 which so diametrically opposed views have been deduced, is espe- 

 cially unsatisfactory, because in the living cell no nucleus is visible, 

 and the polar star of the histological explorer being invisible, all 

 true ideas of direction and course of development are naturally 

 enough shrouded in obscurity. For our part, we have found 

 nothing so suitable as the growing broad ligament of pregnant rats 

 and mice, more especially during a first pregnancy, for there we 

 have a fringe of developing capillaries lying in a thin, rapidly 

 distending membrane, in which the gelatinous matrix is so plentiful 

 and clear that every vessel-forming cell stands out in distinct 

 relief. In that membrane, moreover, the silvei? method of fixing 

 and marking can be applied most favourably, in order to show the 

 junctions of the cells forming, or about to form, the blood-vessels, in 

 the position and shape they possessed when alive. 



