Franklin P. Mall 363 



slide and stained with magenta, show that the elastic fibers are related 

 to the exoplasm of the syncytium much as they are to the reticulum 

 of the lymph follicle. 



It is much more difficult to obtain specimens of the human skin in 

 which the elastic tissue is just beginning to appear. Fresh specimens 

 are not always at hand and preserved specimens are often unsuited to 

 cut into frozen sections which can be boiled or macerated. 



In the skin of a human foetus, measuring 22 cm. from head to breech, 

 practically no elastic fibers are stained by Weigert's method — much 

 as in pig's embryos of the same length. Sections which have been 

 boiled in dilute acetic acid for 4 hours had the white fibrous tissue de- 



If 4 - .-^ 



y s & 







Fig. 16. Fig. 17. Fig. 18. 



Fig. 16. Elastic fibers isolated from the skin of a pig 24 cm. long ( x 250 

 diameters). Magenta. The skin was frozen and cut, then boiled in acetic acid (1^) 

 for one hour. The fibrils form baskets around swollen bundles of white fibers. To 

 them cling nuclei and endoplasm. 



Fig. 17. Elastic network obtained from the skin of a human foetus 22 cm. long 

 ( X 250 diameters). Stained with magenta. The specimen had been hardened in 

 alcohol, was washed in water, frozen, and cut. Sections were then boiled in acetic 

 acid (\<fo) for 4 hours. Further treatment showed that the nuclei and endoplasm 

 could be removed by means of dilute caustic potash, leaving only the delicate elastic 

 fibers. 



Fig. 18. Elastic fibers from the skin of a human foetus 26 cm. long ( x 250 

 diameters). The fresh tissue was cut by the freezing method and boiled in acetic 

 acid (1^) for an hour. It was then coaxed upon a slide and stained with magenta. 

 AH of the fibers have large nuclei clinging to them. 



stroyed completely, leaving only a delicate network of fibers upon which 

 the nuclei lie (Fig. 17). In this specimen it really seemed at first as if 

 there is a complete network formed by the anastomoses of the ends of 

 numerous multipolar cells, but crushing the section and pulling it apart, 

 showed that a delicate network of fibrils remains, which stain with 



