Herrick-Coghill, Nej've Endings in the Skin. 41 



no exception, though it is not always easy to detect the proto- 

 blastic elements. A single theoretical consideration is sufficient 

 to convince one that this is what should be expected, for it is of 

 course recognized that every type of vertebrate has some pro- 

 vision for the constant or occasional removal of the skin. In 

 some cases the process of removal of the corneum is intermit- 

 tent, while in others it is gradual. In either case it is obvious 

 that there must be a proton of undifferentiated material — of 

 cells that have not passed beyond the plastic stage. In those 

 parts of the skin where there is little differentiation between the 

 various layers the difference between the corneum and deeper 

 cells is not readily detected in preparations by the usual pro- 

 cesses, but in the thicker portions where the so-called Leydig 

 cells appear the basal protoblasts are crowded into the inter- 

 spaces and pried apart. One effect of this process has been to 

 stretch the connecting protoplasm into an excessively thin layer 

 or film enveloping the Leydig cell either completely or as a 

 coarse mesh-work of naked protoplasm. In all the preparations 

 we have seen, even those in which the preservation has been as 

 perfect as possible, without the least evidence of shrinkage, the 

 appearance is that of a broad reticulum arising in the intercal- 

 lary or basal protoblasts and enveloping the cell in such a way 

 as to wrap it completely in the products of the adjacent proto- 

 blasts. The most perfect process of preservation for such struc- 

 tures is a combination of chrom-acetic and platinic chloride di- 

 luted in alcohol. The use of Merkel's solution also gave very 

 good results, while the various osmic acid solutions invariably 

 produce too great shrinkage of some parts, especially of the 

 reticulum. In the first mentioned solution it appears that the 

 natural tendencies of the alcohol and the chromic acid counter- 

 act each other while the fixing action of the platinic chloride is 

 in no way interfered with. The avidity to all the usual stains 

 after this treatment is also very great, while in the osmic pre- 

 parations there is not only general diminution of the receptivity, 

 but, what is worse, the effect is not uniform even in the same 

 class of tissue in the same preparation. In properly prepared 

 sections the reticular structure of the protoplasm of the Leydig 



