4 



an exudation from the blood vessels, into which a few migratory 

 cells or leucocytes had found their way. The theory of Kessler, 

 known as the Transudation Theory, found little favor with sci- 

 entists. 



A more generous reception was accorded to a new theory pro- 

 posed by Tornatola at the International Congress of Anatomists, 

 held in Moscow, in 1897. Tornatola asserted that the vitreous body 

 in vertebrates is essentially a fibrous substance, derived exclusively 

 from the retinal cells, and hence an ectodermal formation. His 

 Theory of the Ectodermic Origin of the Vitreous Body found many 

 defenders, such as Rabl, Fischel, Addario, Wolf rum, v. Szily, Mavas, 

 Magitot, Seefelder, and others. According to this theory, the 

 structural parts of the vitreous body consist of a network of very 

 delicate fibers, that have their origin in the supporting cells of the 

 retina and hence are ectodermal. The mesoderm elements are 

 thought to be either leucocytes or true mesoderm cells, having, 

 however, only vaso-formative or nutritive functions and in no way 

 contributing to the production of the vitreous body. 



Lenhossek, in 1902, while admitting the ectodermic origin of the 

 vitreous body, attributed it exclusively to the lens cells and pro- 

 posed his Theory of the Lenticular Origin of the Vitreous Body. 



To reconcile these conflicting opinions, Van Pee and v. Kolliker 

 almost simultaneously expressed the view that the fibrous portions 

 of the vitreous body must be regarded as a complex tissue, to which 

 both ectoderm and mesoderm contribute. According to both these 

 investigators, some of the vitreous fibers originate from the cells 

 of the retina, while the rest are the product either of the extra-ocular 

 mesenchyme (Van Pee) or of the extensive vascular system which is 

 found at certain stages in the development of all mammalian eyes 

 (Kolliker). 



METHODS 



The extreme delicacy of the structure of the vitreous body makes 

 the question of method all-important. Indeed, diversity of opinion 

 regarding the origin, the development, and the structure of this 

 tissue is owing, in large measure, to the methods used. 



In the earlier stages of development, including embryos of 25 

 mm length, most of the ordinary killing fluids were found service- 

 able, Zenker's, Bouin's, and Schaffner's being most frequently used. 



