HISTOLOGICAL METHODS. 169 



these spicules, or from the laceration of the/ tissue due to 

 the knife having come in contact with them. This difficulty 

 is overcome by a thorough saturation of the tissue with gum 

 previous to freezing, as described in 306. 



310. Alterations of the freezing microtome. The freezing 

 microtome was invented and first described by me in the 

 Journal of Anatomy and Physiology, May 1871. The 

 instrument there figured was simply a Stirling's section- 

 cutter, to which I adapted a freezing box. I soon found, 

 however, that the box was too small, the well too large, and 

 the screw imperfect. I therefore altered the apparatus, and 

 described the new form (Fig. 58) in the Lancet (July 1873). 

 The only further alteration that I have made is to have the 

 freezing box entirely covered with gutta-percha, the escape 

 tube (H, Fig. 58) made larger, and the cutting- table made 

 longer between the well and the end nearest the operator. 

 These are real improvements, which make the instrument 

 work in a most satisfactory manner.* At the same time, 

 it may be stated that the identical instrument described in 

 the Lancet has been in daily use in my laboratory for three 

 years. We use no other, because it really has always 

 answered the purpose remarkably well. It has often been 

 suggested that the freezing box should project at the right 

 as well as at the left side of the machine. This arrangement 

 I have carefully avoided from the first, because it interferes 

 with the hand in using the knife, and certainly it is not 

 necessary. 



METHODS OF INCREASING THE TRANSPARENCY OF 

 THE TISSUES. 



311. The transparency of the tissues may be increased 

 i. By impregnating them with fluids which strongly 

 refract light, e.g. glycerine, turpentine, clove oil, Canada bal- 



* The instrument thus modified is made by Mr. Gardner, instru- 

 ment maker, South Bridge, Edinburgh, and I can no longer recommend 

 the instruments of other makers, for they have shown themselves much 

 more disposed to supply the instruments for which they happen to have 

 had "castings" made than to adopt my suggestions.. 



