PART FIFTH. 



EPITHELIAL GLOBULES AND EPITHELIAL 

 SURFACES IN GENERAL. 



WE have studied the nerve globule, which by its prolonga 

 tions places the globular elements of the organism, or of 

 their derivatives, in relation with each other (reflexes) ; and 

 the muscle, which, obeying the motor prolongations of the 

 nerve globule, serves to modify mechanically the relations 

 between the different parts of the organism to each other, or 

 to the outer world ; we have seen that, for this purpose, 

 there are numerous mechanical apparatus attached to the 

 muscle (bones, tendons, ligaments, etc.) ; we have, finally, 

 studied the blood globule, and the blood, which, loaded with 

 the new materials absorbed by certain surfaces of the organ- 

 ism, carries these former into the deeper tissues, while it 

 draws to the excretory surfaces the products of decomposi- 

 tion and of the interior combustion of the organism. We 

 have now, therefore, to study the physiology of these sur- 

 faces, that is, the epithelial globules. 



Anatomically speaking, the epithelial globule is already 

 known to us ; what especially distinguishes it is its relation 

 to the free surfaces of the body; its surfaces are, in fact, 

 formed of membranes, composed of a more or less close pad- 

 ding of connective and elastic fibres, and are covered by an 

 element of which modern anatomy alone has conceived the 

 importance, epithelium. 



It was long believed that the first organ which appears in 

 the embryo, is the nervous system. Modern histological 

 research has proved that the first layer of blastoderm is of an 

 epithelial nature : this layer, in its subsequent development, 

 becomes the intestinal epithelium, the first organic membrane 

 which distinguishes the individual. The importance of the 



