SKIN. 9I 



doubly-stained, one set with picrocarmine and logwood (dammar), and another with picrocar- 

 mine and iodine-green (dammar), p. xlvi. 



() Minute portions of skin may be hardened in a quarter per cent, solution of osmic acid 

 for twenty-four hours, and then preserved in spirit. 



(c) Prepare pieces of the skin of a human fcetus in the same way as (), but keep them 

 only one week in the hardening fluid. 



(</) Place portions of foetal skin in ordinary alcohol. 



(e) A rtificial digestion, p. xxxiv. 



SKIN OF THE PALM. 



Vertical Section. (Picrocarmine.) EXAMINATION (L). Observe the epidermis, consisting 

 of many layers of stratified epithelium. Beneath this the corium, stained bright red, with 

 papillae projecting into the epidermis, which dips down between the papilla?. In the deeper 

 part of the skin note the distinct passage of the connective tissue into that of the subcutane- 

 ous tissue, which latter often contains masses of fat. Perhaps the duct of a sweat-gland may 

 be seen running vertically in the corium, and terminating upwards in a passage which winds 

 its way in a corkscrew-like manner through the epidermis. In the subcutaneous tissue will 

 be found sections of the gland, where it is arranged in the form of a coil. Study these parts. 

 (Indicate the general arrangement in one half of\. XXL, Fig. I.) 



(H). Epidermis. Observe the superficial squames, stained yellow, occurring in many layers 

 (stratum corneuni). They do not appear to contain a nucleus, are flattened, and seen on edge. 

 Beneath this note a clear layer, which does not stain well, and in which the outline of the 

 cells is difficult to make out the stratum lucidum. Immediately below this there lies a layer 

 of granular cells two or three deep, which are deeply stained with carmine, and so stand out 

 brightly the stratum granulosum (Langerhans). Below this observe the layers of more or 

 less polyhedral cells, with their nuclei stained red. Their edges often show prickles. This 

 layer, with those cells that lie below it, constitutes the rete or stratum Malpigkii. Th'e layer 

 of cells resting directly on the corium is composed of small columnar cells with oval nuclei. 

 They seem to be devoid of a membrane. Compare the section of the lip (p. 60) for pigment 

 in these cells. (Indicate these layers of epithelium in PI. XXI., Fig. 2. Their relative position 

 is indicated by letters?) 



These details, and especially the staining of the nuclei with the carmine, are better seen 

 after the preparation has been kept for a week. The nuclei gradually absorb the surplus dye 

 from the Farrant's solution. 



Corium (H). Observe the papillae and the rest of the true skin, all stained of a deep red 

 colour. Note the red-stained bundles of connective tissue running and interlacing in every 

 direction, and amongst them notice the large number of elastic fibres (stained yellow) arranged 

 in the form of a network outside these bundles. Trace the continuity of the connective-tissue 

 bundles of the corium with those of the subcutaneous tissue. Here and there in the papilla; 

 capillary loops of blood-vessels, and perhaps nerves, may be seen. (Fill in papilla in PI. XXL, 

 Fig. 2.) 



Sweat-gland (H). Observe the gland-coil lying in the subcutaneous tissue. Note the 

 gland-tube, cut in all directions. Each tube consists of a basement-membrane, lined by low 

 columnar or cubical cells. Trace a gland-tube upwards through the corium. It consists of a 

 basement-membrane, lined with low columnar epithelial cells, which are continuous with, and 

 are an extension of, the cells of the stratum Malpighii. In all cases the gland passes upwards 



