108 V. E. EMMEL 



also Tschaschin ('13, p. 370), record the observation that in the 

 ease of blood vessels in the vicinity of wounds or other irritants, 

 the vascular endothelium which normally does not stain, may 

 under these changed conditions now react to vital stain. Fi- 

 nally it may be noted that the macrophags themselves do not all 

 react ahke. Thus Tschaschin ('136) recognizes the occurrence 

 of distinct variations in the intensity of the vital stain in the 

 macrophags: "Es muss jedoch hervorgehoben werden, dass die 

 freien Macrophagen der Bauchbohle sich vital bei weitem nicht 

 immer gleich intensiv farben" (p. 351). Tschaschin associates 

 this with variations in different types of stain and methods of 

 injection, rather than as furnishing any ground for identifying 

 these lighter stained cells with detached cells from the peri- 

 toneal endothelium, but in view of the above referred to results 

 by MacCurdy, Evans and Batchlor, it does not appear that the 

 latter possibility can as yet be said to have been successfully elimi- 

 nated. Variations in the vital stain of such detached cells may 

 well be correlated with different degrees of differentiation as 

 has indeed been emphasized even by Tschaschin (p. 382) in con- 

 nection with difference in the vital stain reaction of blood cells 

 so that undifferentiated cells reacting negatively with a given 

 vital stain may with further differentiation give a positive re- 

 action with the same stain. Consequently on the basis of the 

 data so far at hand, the ground does not appear clear on which 

 it can be stated with entire assurance that the mesothelial cells 

 which are able to take up a small number of the granules of the 

 vital stain, may not under given conditions just as in the case of 

 the vascular endothelium, come to manifest an increased ex- 

 pression of the same function such that as detached cells would 

 identify them with true macrophags. ^ 



In conclusion, therefore, it appears that a convincing case can 

 hardly as yet be said to have been made against the possible per- 



2 In connection with the question as to the degree to which mesothelial and 

 endothelial tissue may manifest common morphological and functional pbten- 

 tailities it is of interest to note the results of Hooper and Whipple ('15) indicat- 

 ing that mesothelium as well as endothelium may participate in the formation 

 of bile pigments. 



