TECHNIC. 403 



TECHNIC 



287. Good general views of the skin can be obtained only from sections. 

 Any fixation method may be employed, although alcohol is preferable on 

 account of the better subsequent staining. For detail work Flemming's 

 solution, corrosive sublimate, or osmic acid is the best. Sectioning of the 

 skin is attended with many difficulties, and large pieces can be cut only 

 in celloidin. Small and medium -sized pieces may be cut in paraffin ; but 

 even in this case the skin must be rapidly imbedded in the paraffin /. e. , 

 it must not remain too long in either alcohol or toluol and the paraffin 

 must have only the consistency necessary to cut well (about 50 C. melting- 

 point). In order to obtain good paraffin sections of the skin the follow- 

 ing procedure is recommended : Pieces fixed in Flemming's solution or 

 osmic acid are kept in 96% alcohol, then placed for not more than twenty- 

 four hours in absolute alcohol and imbedded in paraffin by means of the 

 chloroform method. In the chloroform, chloroform -paraffin, and pure 

 paraffin they remain for one hour each. The paraffin used should consist of 

 two parts paraffin of 42 C. , and one part paraffin of 50 C. melting-point. 

 The thermostat must be kept at 50 C. (R. Barlow). The sections 

 should not be mounted by the water-albumen method. 



In sections of epidermis which have been freshly fixed with 

 osmic acid, the stratum corneum may be clearly differentiated into three 

 layers (probably because of the defective penetration of the reagent) 

 into a blackened superficial, a middle transparent, and a still lower black 

 layer (vid. Fig. 326). 



In tissue fixed in alcohol or corrosive sublimate the stratum 

 lucidum stains yellow with picrocarmin, but is very weakly colored by 

 basic anilin stains. In unstained preparations the stratum lucidum is 

 glass-like and transparent. Eleidin is diffusely scattered throughout both 

 the stratum lucidum and stratum corneum. Like keratohyalin, it stains 

 with osmic acid and also with picrocarmin, but not with hematoxylin. 

 Nigrosin stains eleidin, but not keratohyalin. 



Keratohyalin is insoluble in boiling water and is not attacked 

 by weak organic acids. It dissolves, however, in boiling acetic acid, but 

 is not changed by the action of pepsin or trypsin. . The keratohyalin 

 granules of the stratum granulosum swell in from i% to 5% potassium- 

 hydrate solution ; under the influence of heat these granules together with 

 the cells containing them are finally dissolved. They are not attacked 

 by ammonia, and remain unaffected for a long time in strong acetic acid. 

 As ammonia and acetic acid render the remaining portions of the tissue 

 transparent, these reagents may be employed for the rapid identification 

 of keratohyalin. The larger flakes of keratohyalin swell in sodium car- 

 bonate solution (i%), but not the smaller granules, and it would seem 

 that the larger granules have less power of resistance than the smaller. 

 Keratohyalin remains unchanged in alcohol, chloroform, and ether, but 

 is digested in trypsin and pepsin (not, however, the keratin). Kerato- 

 hyalin can be stained with hematoxylin and most of the basic anilin dyes. 



The prickles of the cells composing the stratum Malpighii may 

 be seen in very thin sections (not over 3 /;. in thickness) of skin previ- 

 ously fixed in osmic acid. In this case it is best to employ not Canada 

 balsam, but glycerin, which does not have so strong a clearing action. 

 Isolation of the prickle cells is best accomplished as follows (Schieffer- 



