No. 635] THE HAIR OF MAMMALS 521 



ment, however, was found to consist in washing the hair 

 in the ether-alcohol, drying, immersing in xylol, and then 

 mounting in very thin Canada balsam. This makes a 

 permanent mount. 



Lighting with the dark ground illumination was found 

 to give the best results in the examination of the external 

 configuration of the medulla. 



In the case of hairs where the heaviness of the pigmen- 

 tation obscures the medulla, or in compound-medullated 

 hairs, or in those cases where an accurate knowledge of 

 the form of the cross section of the medullary column is 

 desired, it is necessary to prepare cross sections of the 

 hair shaft, by the usual methods of imbedding in paraffin 

 or celloidin. 9 Figs. 188 and 189 show the manner in 

 which the form of the medulla is shown in transverse 

 sections, as well as its relations to the thickness of the 

 cortex and of the cuticle. 



The methods used to make clear the medulla serve well 

 also to reveal the pigment granules. In examination of 

 the shaft for these tiny bodies the 1.8 mm. objective and 

 the lOx eyepiece with the draw tube of the microscope 

 extended its full length was found to be the lowest power 

 which could be satisfactorily employed. Lighting with 

 daylight glass and a 200-watt tungsten-filled bulb was 

 apparently a necessity. 



The cortex, because of its nearly homogeneous struc- 

 ture, was not found to exhibit characters which could be 

 used as criteria for identification. Fig. 187 shows a hair 

 macerated in caustic soda, and with the cortex teased out 

 to show the distorted, elongated cortical cells, or hair 

 spindles. 



The use of caustics and strong acids for dissociating 

 the cuticular scales is not recommended. The softening 

 of the scales distorts their form and thus renders them 

 useless for delicate determinative purposes. 



It very often becomes necessary to distinguish the dis- 



