X. 



EPITHELIAL AND ENDOTHELIAL TISSUE. 



THE ideas concerning the character of epithelium and endo- 

 thelium, as presented here, are widely different from the 

 opinions usually held upon this subject. The light of the bio- 

 plasson theory has been brought to bear upon a subject hitherto 

 but little understood. All the views here advanced have been 

 taught by me in my laboratory for over seven years, and these 

 views were in part published in 1878.* 



Definition. A single living plastid, for instance, an amoeba, 

 a colorless blood-corpuscle, or a pus-corpuscle, with high mag- 

 nifying powers of the microscope, exhibits a delicate, net-like 

 structure, both within the nucleus and in the surrounding body. 

 The body is inclosed by an extremely thin, shining, homogeneous 

 layer, and a layer of this kind always lines the vacuoles seen, 

 temporarily or permanently, in a creeping plastid. The net-work 

 of the body inosculates with both the peripheral layer and that 

 inclosing a vacuole. The reticulum of the nucleus, its surround- 

 ing envelope the net- work of the plastid, the covering and 

 lining layers, both of the body and its vacuoles, are formations 

 of living matter, the active contraction and passive extension of 

 which cause locomotion and all changes of form during the life 

 of the plastid. 



In the germinal disk of the more highly developed animals, 

 which arises from two symmetrical halves of the impregnated 



* " Epithelium and its Performances." A paper read before the American 

 Dermatological Association, at their meeting in Saratoga, August 27, 1878. 

 Published in abstract. New York Medical Journal, 1878. 



