THE SKIN. 379 



followed by treatment with crude pyroligneous acid. For the salaman- 

 der Hermann recommends a mixture composed of i % platinum chlorid 

 15 c.c. , 2% osmic acid 2 c.c., and glacial acetic acid i c.c., and for 

 mammalia the same solution with double the amount of osmic acid. 

 The fluid is allowed to act for some days, the specimen then being 

 washed for twenty-four hours in running water and carried over into alco- 

 hols of ascending strengths. Paraffin sections are treated as follows : 

 Place for from twenty-four to forty-eight hours in safranin (safranin i 

 gm. is dissolved in 10 c.c. of absolute alcohol and diluted with 90 c.c. 

 of anilin water). After decolorizing with pure or acidulated absolute 

 alcohol the sections are placed for three or four hours in gentian-violet 

 (saturated alcoholic solution of gentian -violet 5 c.c. and anilin water 

 100 c.c.), and are then placed for a few hours in iodo-iodid of potassium 

 solution until they have become entirely black (iodin i, iodid of potas- 

 sium 2, water 300); finally, they are washed in absolute alcohol, until 

 they become violet with a dash of brown. The various structures appear 

 differently stained : for instance, the chromatin of the resting nucleus 

 and of the dispirem, bluish-violet ; the true nucleoli, red ; while, on the 

 other hand, in the aster and diaster stages the chromatin stains red. 



It is of especial importance that small testicles should not be cut into 

 pieces before fixing, as this causes the seminal tubules to swell up and 

 show marked changes, even in regions at some distance from the cut 

 (Hermann, 93, I). 



The treatment of the remaining parts of the male reproductive organs 

 requires no special technic. 



VI. THE SKIN AND ITS APPENDAGES. 



A. THE SKIN (CUTIS). 



THE skin consists of two intimately connected structures the 

 one, of mesodermic origin, is the true skin, corium or dermis ; the 

 other, of ectodermic origin, is the epidermis or cuticle. The super- 

 ficial layer of the corium is raised into ridges and papillae which 

 penetrate into the epidermis, the spaces between the papillae being 

 filled with epidermal elements. Thus, the lower surface of the 

 epidermis is alternately indented and raised into a system of furrows 

 and elevations corresponding to the molding of the corium. 



In the epidermis two layers of cells may be observed the 

 stratum Malpighii, or stratum germinativum (Flemming), and the 

 horny layer, or stratum corneum. According to the shape and 

 characteristics of its cells, the stratum germinativum may also be 

 divided into three layers first, the deep or basal layer, consisting 

 of columnar cells resting immediately upon the corium ; second, 

 the middle layer, consisting of polygonal cells arranged in several 

 strata, the number of the latter varying according to the region of 

 the body ; and third, the upper layer, or stratum granulosum, 

 which is composed, at most, of two or three strata of gradually 

 flattening cells characterized by their peculiar granular contents. 



