SQUAMOUS EPITHELIUM. MITOSIS. 29 



arrest its progress when sufficiently developed by running 

 water through until the diffuse colour is removed. Note 

 films of precipitated mucin and also salivary corpuscles. 



Human Skin. V.S. (p. 11, s. 22 & 24, c. P., m. B.) 



(L) Note the epidermis resting upon and filling up the 

 irregularities of the dermis. The epidermis consists of two 

 main layers the horny layer, externally, resting upon the rete 

 mucosum, from which it is sharply defined by the thin stratum 

 lucidum. 



(//) In the lowest layers of the rete mucosum the cells are 

 elongated (germinal cells), those above being polygonal, and 

 the highest somewhat flattened and of a granular appearance 

 (stratum granulosum). The cells composing these layers are 

 united to each other by numerous fine filamentous bridges, 

 hence named "prickle cells." A continuous system of channels 

 is thus left between the cells up to the stratum lucidum for 

 the percolation of lymph (formation of a blister). 



The stratum lucidum is formed by the accumulation of eleidin 

 produced by the cells of the stratum granulosum. It can be 

 detected accumulating as a thin layer between them, gradually 

 thickening to a continuous layer in which cell outlines are lost. 

 The cells of the horny stratum are much flattened and com- 

 pressed ; they are the dead remains of the malpighian cells, and 

 do not exhibit marked differential staining. Excepting in rare 

 instances no traces of nuclei are visible. Osmic acid blackens 

 the inner and outer portions of the horny layer. 



Mitosis. Nuclear filaments from the salivary cells of the 

 chyronomus larva. A common inhabitant of the mud of 

 stagnant waters. It is about half an inch long, red in colour, 

 and progresses by jerky unbending from a C shape. 



Pull the head off with forceps, cover in normal saline, irri- 

 gate with an aqueous 2 pc> solution of methyl green until 



