69 



156. Hair muscle. (Arrector pili). Cat. Section of the skin 

 from the dorsal side of the tail, cutting the hairs longitudinally. 

 Picric alcohol ; collodion ; sections //. Stain with hematoxy- 

 lin and picrofuchsin. 



This preparation will illustrate especially the hair muscles and 

 their relation to the hair follicles. Study, noting their relation to 

 the follicles and sebaceous glands ; their large size in this prepara- 

 tion. Understand their action in raising the hair. Compare 154, 

 identifying in it the hair muscle. 



MAMMARY GLAND. 



157. Mammary gland. Cow. In lactation. ; 

 parafiBn ; sections fx. Stain with hematoxylin and eosin. 



Observe carefully the general structural appearance of the 

 gland, noting the lobulation and the secreting acini. Study care- 

 fully the epithelium forming the acini, noting the character of the 

 cells and their appearance and indications of functional activity. 

 Note also the secretion (if present) in the lumen of the acinus. Com- 

 pare with 158 and 159. 



158. Mammary gland. Cow. In lactation. 1% osmic acid 

 (§ 22) ; paraffin ; sections fA.. No staining. 



This preparation supplements 157. The osmic acid blackens 

 the fat globules which in 157 were dissolved out. Observe the num- 

 ber and size of the globules iu the epithelial cells of the acini and 

 in the secretion in the lumen of the acinus. 



159. Mammary gland. Cow. Not in lactation ; 

 paraffin ; sections /t. Stain with hematoxylin and eosin. 



This section is to be compared with 157, the identity of struc- 

 ture noted, and the different appearance of the acini due to the 

 resting condition of the cells. 



