194 EPITHELIAL GLOBULES. 



B. The lymphatic system considered as an adjunct to the 

 epithelial functions. 



If the epitheliums are essentially living, they must and do 

 undergo continual changes.' Beside the young cells we ought 

 to find old cells, and numerous fragmentary remains of the 

 same; we may be sure that every epithelial globule which 

 exists has been in its place only a short time, and will soon 

 disappear to make room for another; its fundamental char- 

 acter is its ephemeral existence. This fall, this constant 

 change of the epithelial cells is really the means by which 

 some of them fulfil their functions : thus the epitheliums 

 of the glandular culs-de-sac are destined to fall continually 

 into deliquium, and thus constitute the phenomenon of secre- 

 tion. 1 



Apart from the glands, however, the fall of the epitheliums 

 is not a function, but simply a result of their existence. In 

 the epidermis which covers the cutaneous surface, this fall 

 takes place under the form of furiuraceous desquamation, 

 that is, small horny scales (a collection of old, dried-up 

 epidermal cells). 



In the mucous membranes desquamation takes the form 

 of a thick ropy fluid product, mucus, which has given its 

 name to this large class of membranes. The mucus is less 

 abundant in the normal than in the pathological condition, 

 in which, we might say, the life of the cells is suddenly closed. 

 It is a hyaline elastic substance, resembling the exterior of 

 the eggs of the batrachians, insoluble in water, coagulable by 

 acids, but easily dissolved in alkaline fluids ; the application 

 of an alkali to the epithelial membranes has the effect of 

 dissolving the cellular elements under the form of mucus. 

 The chemical composition of the mucus is nearly the same as 

 that of albumen ; indeed the albumen of the white of eggs is 

 only mucus of the genital organs of the bird. 



The so-called mucous glands generally secrete fluids which 

 are very tenuous, and miscible with water, and thus differ 

 greatly from the mucus ; the latter is not the product of any 

 special gland, but is the result of the desquamation and 

 fusion of the epithelium ; but this shows that we may expect 

 to meet with all the transitions between the mucus properly 

 so called, and the various products of special secretions 



1 See V. Billet, " Ge'ne'ralites sur les secretions." These de 

 doctorat, Strasbourg, 1868, No. 129. 



