LUBRICATING TISSUES 



399 



they pour out a fluid that is used principally to keep the skin moist and 

 to reduce surface heat by evaporation. These glands are simple tubular 

 glands which are continuous with the basal cells of the stratified epithe- 

 lium. The duct reaches up through the outer layers of this epithelium 

 to open at the surface. 



The gland itself passes down into the connective tissue of the skin 

 and ends as a coil of somewhat similar structure. This structure con- 

 sists, in the duct, of two or three layers of cells which constitute a weakly 

 stratified layer. The lumen thus formed is bounded by a cuticle belong- 

 ing to the inner layer of cells. A distinct basal membrane appears 

 between the epithelium and the surrounding connective tissue, and on 

 this are a few longitudinal smooth muscle fibers. 



The lower coiled part of the tube is lined by a single layer of cubical 

 or columnar cells which do the active secretion. Several phases of activ- 

 ity may be detected in them, and it is known that, while under ordinary 

 conditions they secrete an oily material to lubricate the skin, when ex- 

 cited by the proper nervous stimuli and blood supply, these glands pour 

 out the watery sweat, probably in addition to the first material. 



The sweat glands attain a large size in certain positions, and in some 

 of these larger forms the secretion is probably different. One kind of 

 modification is probably the very large wax glands found in the ear tube. 

 In structure these are very much the same as sweat glands. In function 

 they secrete and discharge a thick oily material that almost solidifies 

 upon contact with the air and serves as a protection to the ear tube 

 against the entrance of harmful insects or foreign particles. Figure 

 363 shows a section of the epi- 

 thelium lining the coiled por- 

 tion of this wax gland with the 

 secretion shown in situ in the 

 lumen. 



See also the description of 

 the mammary glands in Chap- 

 ter XXIII, as they are also 

 probably derived from primitive 

 sweat glands. 



Technic. Flemming's fluid 

 and thin paraffin sections will 

 give the best results with nearly 

 all of these tissues. The oily 

 secretions are sometimes stained black, and sometimes not, by the 

 osmic acid. When the lubricating secretion is a mucin, it is best to 

 use sublimate or some similar fixative, and then to stain with one of 

 the dyes that is specific for this substance. Most beautiful differentia- 



FlG. 363. Transverse section through one of the 

 secretory coils of a wax gland in the cat's ear- 

 tube. Some secreted material lies in the lumen. 



