324 



PRACTICAL HISTOLOGY. 



[XXIX. 



10. Elements of a Hair (H). Place a small piece of a hair in 

 a drop of strong sulphuric acid. Cover and press lightly with a 

 needle. Be careful to avoid letting a drop of the acid fall on the 

 brasswork of the microscope. The hair splits up longitudinally 

 into what look like fibres, but by gentle tapping on the cover they 

 split into cells, so that a hair is composed of epithelial cells joined 

 together, having previously undergone conversion into keratin. 



11. Babbit's Hair (H). Mount in balsam. This hair contains 

 one or more rows of cubical cavities containing air. The cavities 

 appear black, and are surrounded by a small quantity of cortex. 



12. Wool (Lesson I. 10). 



FIG. 310. T.S. One-half of a Hair in its 

 Follicle ; a. Outer, c. Inner fibrous 

 sheath ; b. Blood-vessels ; d. Hya- 

 line layer; e. Outer, /, g. Inner 

 root-sheath (/. Henle's layer, g. 

 Huxley's layer) : h. Cuticle ; I. 

 Hair. 



FIG. sii.-V.S. Injected Skin, Palmar 

 Surface of Finger. 



Blood- Vessels of the Skin. V.S. of a piece of skin cut from a 

 limb injected with a gelatine mass. They must not be too thin. 

 After injection the skin is hardened in Miiller's fluid and afterwards 

 in alcohol (three weeks). Mount (balsam) a section of the palmar 

 surface of a finger, and one from the general surface of the body. 



A good injection-mass is a watery solution of china-ink. It is 

 rubbed down on a hone until a moderately thick black solution is 

 obtained, so that when a drop is placed on blotting-paper it holds 

 together, and no grey ring is formed round the drop. It has this 



