92 PRACTICAL HISTOLOGY. 



between two papillae. From the epidermis it pursues a spiral course. Each sweat-gland 

 consists of a simple tube, composed of a coiled portion the gland proper situated in the 

 subcutaneous tissue, and a duct, which passes more or less vertically through the corium, to 

 open on the surface of the epidermis. A brightly refracting membrane seems to line the 

 duct in its passage through the epidermis. In the corium, the duct consists of a membrana 

 propria, and inside this are two or three layers of polyhedral nucleated cells, which are 

 separated from the comparatively narrow lumen by a homogeneous bright membrane. In the 

 coiled part, the tube (proximal) is lined with similar cells, but in the other, or distal part, the 

 membrana propria is very thin, and it is lined with a single layer of columnar nucleated cells, 

 which are striated longitudinally. (Indicate a section of sweat-glands in PI. XXL, Fig. 3.) 



Touch-corpuscles (Wagner) may be found in some of the papillae. They arc oval bodies, 

 made up of fibrous tissue, and form one of the ' end organs,' or structures in which the nerves 

 of the skin terminate. 



In the subcutaneous layers sections of Pacinian corpuscles may be found (p. 46), but they 

 will be more easily found in the fcetal skin. (Indicate a section of one in PI. XXL, Figs. I and 3.) 



DOUBLE-STAINING OF THE SKIN. 



This is a most excellent method for revealing the different structures. 



1. Picrocarmine and Logwood. Make vertical sections of the skin of the heel of a foetus, 

 and stain it first with picrocarmine. Wash the section in water slightly acidulated with acetic 

 acid, and then wash it thoroughly in ordinary water. Stain it slightly in logwood and mount 

 in dammar. 



The superficial layers of the epidermis are yellow, the deep layers and sweat-glands are a 

 logwood tint, and the connective tissue is red. 



2. Picrocarmine and Iodine-green. Proceed as before, but use a very dilute solution of 

 iodine-green (p. xliv) instead of the logwood. Mount in dammar. 



The superficial layers of the epidermis are yellow, the deep layers, the sweat-glands, nuclei 

 of the fat-cells and connective-tissue corpuscles are green, whilst all the connective tissue is 

 red. These doubly and trebly stained sections are very instructive. In these sections one 

 is almost sure to meet with numerous sections of Pacinian corpuscles (p. 46). Note also 

 the relatively larger number of sweat-glands in the fcetal skin (compare p. 27). 



For the development of fat-cells see p. 27. 



DIGESTION OF THE SKIN. 



This method was introduced into histology several years ago by the author. It is invalu- 

 able for ascertaining the arrangement of the elastic fibres and muscular tissue in the skin. It 

 has recently been adopted by Kiihne for investigating the structure of nerves. It depends for 

 its value on the fact that certain substances are digested more rapidly than others, and so are 

 rapidly removed. 



Make an artificial gastric juice by mixing I c.c. of pure hydrochloric acid with 500 c.c. 

 water, and add one gramme of pepsine, or a few drops of a glycerine extract of the gastric 

 mucous membrane. It is well to keep the mixture at 38 C. for two or three hours before 

 using it. The piece of skin to be digested is stretched over a small glass ring and firmly tied 



