ORGANS OF THE SENSES AND THE COMMON INTEGUMENT 



which are soft, opaque, granular, and soluble in acetic acid. These are known as 

 prickle cells because of the bridges by "which they are connected to one another. 

 They contain fine fibrils which are continuous across the connecting processes 

 with corresponding fibrils in adjacent cells. Between the bridges are fine inter- 

 cellular clefts serving for the passage of lymph, and in these lymph corpuscles or 

 pigment granules may be found. 



The stratum granulosum comprises two or three layers of flattened cells which 

 contain granules of eleidin, a substance readily stained by hematoxylin or carmine, 

 and probably an intermediate substance in the formation of keratin. They are 

 supposed to be cells in a transitional stage between the protoplasmic cells of the 

 stratum mucosum and the horny cells of the superficial layers. 



The stratum lucidum appears in section as a homogeneous or dimly striated mem- 

 brane, composed of closely packed cells in which traces of flattened nuclei may be 

 found, and in which minute granules of a substance named keratohyalin are present. 



Stratum corneum- 



Stratum lucidum j 

 Stratum granulosum { 



I 



Stratum mucosum 



" Nerve fibrils 



Stratum germinativum 



Fio. 941. Section of epidermis. (Ranvier.) 



The stratum corneum (horny layer) consists of several layers of horny epithelial 

 scales in which no nuclei are discernible, and which are unaffected by acetic acid, the 

 protoplasm having become changed into horny material or keratin. According to 

 Ranvier they contain granules of a material which has the characteristics of beeswax. 



The black color of the skin in the negro, and the tawny color among some of 

 the white races, is due to the presence of pigment in the cells of the epidermis. 

 This pigment is more especially distinct in the cells of the stratum mucosum, and 

 is similar to that found in the cells of the pigmentary layer of the retina. As the 

 cells approach the surface and desiccate, the color becomes partially lost; the 

 disappearance of the pigment from the superficial layers of the epidermis is, 

 however, difficult to explain. 



The pigment (melanin) consists of dark brown or black granules of very small 

 size, closely packed together within the cells, but not involving the nucleus. 



The main purpose served by the epidermis is that of protection, as the surface 

 is worn away new cells are supplied and thus the true skin, the vessels and nerves 

 which it contains are defended from damage. 



