THE SKIN. 127 



LESSON XXV. 



THE SKIN. 



1. SECTIONS of skin from the palmar surface of the fingers. The sections are 

 to be made vertical to the surface, and should extend down as far as the sub- 

 cutaneous tissue. They may be stained with hsematoxylin or picro-carmine 

 and mounted in Canada balsam. In these sections notice the layers of the 

 epidermis and their different behaviour to the staining fluid. Notice also the 

 papillae projecting from the corium into the epidermis, and look for tactile 

 corpuscles within them. In very thin parts of the sections the fine inter- 

 cellular channels in the deeper parts of the epithelium (see Lesson VI. p. 27) 

 may be seen with a high power. The convoluted tubes of the sweat-glands 

 will be seen here and there in the deeper parts of the corium, and in thick 

 sections the corkscrew-like channels by which the sweat is conducted through 

 the epidermis may also be observed. Make a sketch showing the general 

 structure under a low power, and other sketches to exhibit the most important 

 details under a high power. Measure the thickness of the epidermis and the 

 length of the papillse. 



2. Sections of the skin of the scalp, vertical to the surface and parallel to 

 the slope of the hair-follicles, and others parallel to the surface, and therefore 

 across the hair follicles. Stain and mount in the same way as in the last 

 preparation. Examine also the structure of the hairs. 



In these preparations the details of structure of the hairs and hair-follicles 

 together with the sebaceous glands and the little muscles of the hair-follicles 

 are to be made out. 



3. Vertical sections across the nail and nail-bed, ciit with a strong razor. 

 To cut such hard structures as the nail it is best to soak the tissue in strong 

 gurn arabic for a few days, then place it in an appropriate position upon a cork 

 or on the object-carrier of a microtome, and plunge the whole into 70 per 

 cent, alcohol. This renders the gum hard, and enables sections to be cut of 

 sufficient fineness. To remove the gum the sections are placed in water for a 

 few hours ; they may then be stained with hematoxylin or picro-carmine and 

 mounted in the usual manner in Canada balsam. Notice the ridges (not 

 papillae) of the coriuin projecting into the epidermis. Observe also the 

 distinction of the epidermis into Malpighian layer and nail proper. 



4. Mount in Canada balsam a section from a portion of skin of which the 

 blood-vessels have been injected, and notice the distribution of the capillaries 

 to the sweat-glands, to the hair-follicles, and to the papillary surface of the 

 corium. 



The skin is composed of two parts, epidermis and cutis vera. 



The epidermis, or scarf skin, is a stratified epithelium (fig. 151). It 

 is composed of a number of layers of cells, the deeper of which are soft 

 and protoplasmic, and form the rete mucosum of Malpighi, whilst the 



