CELLULAR ELEMENTS OF THE MAMMALIAN EMBRYO 107 



tain a stain reaction for either the macrophags of the peritoneal 

 cavity or the peritoneal epithelium, a result which, as he him- 

 self notes (p. 239) consequently substantiates Schott's conclu- 

 sion. On the other hand it has been shown that in cases where 

 the macrophags do manifest a typical vital stain reaction the 

 reaction of the mesothehum is by no means necessarily entirely 

 negative, for Evans ('14) records the observation that whenever 

 certain cells such as the clasmatocytes (resting wandering cells) 

 of the connective tissues and macrophags of the great serous 

 cavities "react in a typical intense manner to the vital stain" 

 other cells ''are normally found with much smaller often verj'^ 

 minute granules of the stain" in which latter class, it is import- 

 ant to observe, is included the mesothelium ''hning the peri- 

 toneum and covering its organs" (p. 100). Again it does not 

 appear that the fact that the reaction of a tissue to the vital 

 stain in a given case is negative or stains only shghtly in con- 

 trast to the macrophags necessarily leads to the conclusion that 

 such a tissue cannot give rise to the macrophag elements. A 

 case in point is that of the endothelium of some of the larger 

 blood vessels in the liver. It has been shown for example by 

 Taschaschin ('13) that whereas after 'Kallargol' injection black 

 silver granules are specifically deposited in the large mononu- 

 clear elements or macrophags of the blood, they are not found 

 in the endothelial cells of the portal vessels (p. 353). On the 

 other hand Batchelor ('14) , while he finds that injections of try- 

 pan blue just as in the case of 'KallorgoF ,do not normally stain 

 the endothelium of the larger portal vessel of the liver in con- 

 trast to the positive reaction of some of the phagocytic endothe- 

 lial giant cells in the same organ, nevertheless endothelial pro- 

 liferations experimentally produced in the same vessels by means 

 of albumen emboli do react to the stain: thus newly formed en- 

 dothelial tissue at the site of the embolus and in its immediate 

 neighborhood it is stated, ''is stained vitally, a phenomenon 

 never seen with the normal endothelial cells of larger vessels, 

 and showing that the vital stain is adequate for the detection of 

 endothelial growths although the parent tissue does not show this 

 property" (p. 139). MacCurdy and Evans ('12, p. 1695— and 



