272 THE AMEKICAN MONTHLY [December, 



saw moistened in spirit. The section may then be rubbed down to the 

 necessary thinness on a hone, the balsam dissolved out in benzole, and 

 the section mounted in the solution of Canada bfClsam. 



Section cutting also includes that of the soft tissues. As it is desir- 

 able sometimes to make sections of the hard tissues in conjunction with 

 the soft parts attached to them, and as it is not possible to grind sec- 

 tions in the manner just described, recourse is had to decalcification, by 

 which the lime is removed, and the bony tissues rendered soft enough 

 to be cut with a razor. There are various solutions of acids by which 

 this process is carried out, but the readiest and most efficient agent for 

 this purpose is a saturated solution of common alum to which has been 

 added a few drops of hydrochloric acid to each ounce of solution. 

 While in this mixture the acid dissolves the lime, the alum hardens the 

 soft tissues, so that, in a short time, it is possible to cut very thin sec- 

 tions, showing all the relations between the soft and hard elements of 

 a structure — such sections requiring only very profuse washing to free 

 them from the chemicals before they are ready for staining and mount- 

 ing. There are other substances from which sections may be made 

 which occupy an intermediate position between the hard and soft tis- 

 sues, such as hair and cartilage, and it will be desirable to speak of 

 them before describing the preparation of sections from soft tissues. 



Hairs are horny cylindrical structures springing from a papilla situ- 

 ated at the end of a tubular depression of the skin, and in investigating 

 their histology, these two structures, viz., the hair and its follicle, should 

 be studied in conjunction. This can be done by sections taken in two 

 directions, and by the use of suitable reagents. There are two methods 

 by which horizontal sections of hair are made, one being to arrange a 

 bundle of hairs longitudinally, and soak it in glue; when this has set 

 the bundle may be cut into thin slices with the microtome, the glue dis- 

 solved, and the sections picked out for mounting in Canada balsam. 

 The other plan is to shave the beard very closely with a keen razor, and 

 after a few hours to shave again. In this manner very thin horizontal 

 sections of hair, and a very fair sprinkling of oblique sections may be 

 obtained. Vertical sectionsthrough the hair follicle, showing the struct- 

 ure of the root of the hair, may sometimes be purchased ; but in many 

 cases the anatomical details are so obliterated in the mounting, that it 

 becomes advisable to make them if we would see the relations of the 

 hair to its follicle and to its surrounding histological elements. 



Portions of the scalp, or such other hairy parts of an animal as afford 

 the requisite depth of substance for the follicle, may be cut into small 

 cubic portions, placed in ammonium chromate, and examined from day 

 to day till sufficiently firm to cut into sections. Choose a piece in which 

 the line of section corresponds with the direction of the roots of the 

 hairs. A section may then be produced which will show all we need. 

 Fairly good specimens of the roots of hair may be obtained by slowly 

 drawing out a hair of the beard, which occupies the centre of a pimple. 

 The inflammation and consequent effusion of fluid into the surrounding 

 tissues so loosens the root of the hair that it may be readily detached, 

 bringing with it parts of its sheath and the cells. These preparations 

 should be stained with carmine and mounted in glycerine. 



Cartilage is another semi-hard sulDstance which occupies an inter- 

 mediate position between the hard and soft tissues, requiring no prepa- 



