364 The Development of the Connective Tissues 



magenta, is jDartly buried in the gelatinous remnant of the white fibrous 

 tissue, and is partly covered with nuclei and endoplasm. The elastic 

 network can be further isolated by boiling the section in a dilute solu- 

 tion of caustic potash; the delicate elastic fibers alone remain, the white 

 fibers and nuclei having been removed completely. 



The skin of a foetus 7 months old (36 cm. long) has wdthin it many 

 delicate elastic fibers which are stained by Weigert's method. The 

 individual fibrils are in general parallel with the bundles of white 

 fibrils, are not composed of rows of individual granules, but are homo- 

 geneous. When the sections are boiled to remove the white fibers in 

 part and then stained by Weigert's method, a beautiful network remains, 

 one or two fibrils accompanying each swollen bundle of white fibrils. 

 Frozen sections boiled in dilute acetic acid and stained with magenta 

 give the same picture. The oval nuclei with the surrounding endoplasm 

 lie upon the elastic fibrils, surround them, but are not continuous 

 with them (Fig. 18). Similar results have been obtained by Jores, 

 who studied the formation of elastic fibers in a myxoma.'" 



The elastic fibers have increased greatly in number in the skin of 

 a fcetus 8 months old. The fibers are closely packed to form baskets 

 encircling the individual bundles of Avhite fibers. Specimens made by 

 the aid of boiling acetic acid are again most instructive, for in such 

 specimens the fibers are isolated with nuclei and endoplasm clinging to 

 them. Thick sections made in this way appear as a felt in which 

 there are numerous holes, where the bundles of white fibers lay, with 

 nuclei and endoplasm clinging to the elastic fibers. In the skin at 

 birth the elastic fibers have become a little larger and denser, and 

 therefore more numerous as the skin has expanded and become thicker. 

 Frozen sections which have been treated with boiling actic acid and 

 stained in magenta show nuclei and endoplasm attached to the indi- 

 vidual fibers. Sometimes they are spindle-shaped but usually they form 

 plates which are easily separated from the elastic fibrils after the white 

 fibers have been dissolved. 



In the skin of an infant two months old the elastic and white fibrous 

 tissues are about equal in quantity. The elastic fiber baskets encircle 

 and frequently sink into the bundles of the white fibers, as is easily 

 shown in sections which have been stained by Weigert's method. The 

 same picture is seen in the skin of infants from two to six months old. 



While the elastic fibers are present in relatively small number in 

 the skin of a foetus 22 cm. long, and gradually increase in size and 



4 



'6 Jores, Ziegler's Beitrii^e, xxvii, Fig. 3. 



