THE FROG: HISTOLOGY, GERM CELLS, DEATH 97 



disposed in groups of two or four formed by the division of 

 one original cell. As these secrete additional ground sub- 

 stance they become pushed apart by it. In calcified cartilage 

 the structure is the same as in hyaline, but the ground 

 substance is impregnated with salts of lime. Connective 

 tissue, like cartilage, has a ground substance which stains 

 readily with silver nitrate, but it is much softer and always 

 contains fibres of two kinds — white fibres, which have a 

 wavy course, branch but do not join, and are composed of 

 extremely fine fibrils, and yellow or elastic fibres, which have 

 a straight course, branch sharply and join to form a mesh- 

 work, and are not composed of fibrils. The white fibres 

 swell up and become transparent in acetic acid, the elastic 

 fibres do not. When 

 connective tissue is 

 boiled, the ground 

 substance yields 

 gelatin, whereas car- 

 tilage treated in the 

 same way gives a 

 substance known as 

 chondrin. In the 

 ground substance 

 are a number of ir- 

 regular spaces occu- 

 pied by cells or con- 

 nective-tissue corpus- 

 cles, of which some 

 are branched and »••> Artery; c.t. 

 often continuous by 

 their branches, while 

 others are rounded and granular. Connective tissue pene- 

 trates every part of the body, holding together the softer 

 tissues and forming in the skin a continuous envelope 

 known as the dermis, which is covered by the epithelial 

 layer, known as the epidermis, already described (p. 92). 

 Tendon is a modified form of connective tissue in which 

 the white fibres are very plentiful and run parallel instead 

 of forming a feltwork. The cells lie in rows between the 

 fibres. Fatty or adipose tissue is a form of connective 

 tissue in which the fibres are scanty and most of the cells 



Fig. 56. — A transverse section of a medul- 

 lated nerve of the frog, stained with 

 osmic acid and magnified. 



connective-tissue sheath or peri- 

 neurium ;/"., funiculus or bundle of nerve fibres ; 

 vein. 



