XXX.] SPINAL CORD. 333 



the human cord. The same methods are applicable to both. 

 Remove the whole length of the spinal cord from a cat, taking care 

 not to squeeze or crush it in the process. Make transverse cuts 

 into it about f of an inch apart, and suspend it in a tall vessel in a 

 large quantity of Miiller's fluid, or 2 per cent, ammonium or 

 potassium bichromate. Keep it in a cool place in the dark. 

 Bichromate of ammonium hardens the cord very slowly indeed. 

 In fact, to get a properly hardened cord months are required. To 

 test if the cord is properly hardened, cut a section of the cord taken 

 from the ammonium bichromate fluid, place it in water, and if it 

 curls up, it is not properly hardened. It ought to remain flat. 

 The process may be expedited by hardening first for 4 or 5 weeks 

 in the bichromate, and completing the hardening for 2-3 weeks in 

 J per cent, chromic acid. Change the hardening fluid on the 

 second day, and repeatedly thereafter. After 4-5 weeks, when it 

 becomes tough, wash it, and harden in the various strengths of 

 alcohol, beginning with 50 per cent. If, however, the spinal cord 

 is to be used for Weigert's haematoxylin stain, it must not be 

 washed in water, but placed in alcohol direct from the Miiller's 

 fluid or potassic bichromate. 



T.S. are made from the cervical, dorsal, and lumbar regions. 

 They may be made by means of the freezing microtome, the cord 

 having been previously saturated in the sugar and gum mixture ; 

 or small pieces of the cord may be stained in borax-carmine 

 (i week), and then cut in paraffin. Or they may be embedded and 

 cut in celloidin, and afterwards stained (p. 60). The paraffin' 

 sections are fixed to a slide by a "fixative/' the paraffin removed 

 by turpentine or xylol, the sections clarified by clove-oil, and 

 mounted in balsam. Sections, if made by freezing, may be stained 

 with carmine, hsematoxylin, aniline-blue-black, safranin, methylene- 

 blue, or by other methods. 



1. T.S. Spinal Cord of Cat (L) and (H). Speaking broadly, 

 the same general arrangement obtains as in fig. 314. Suppose it to 

 be the dorsal region, and the cord to be stained in carmine and 

 mounted in balsam, observe : 



(a.) (L) The nearly circular outline of the section, covered 

 externally by the pia mater, composed of two layers. From its 

 under surface septa run into the white matter of the cord, and some 

 of them carry blood-vessels, and processes pass into the fissures of 

 the cord. 



(/>.) The anterior and posterior median fissures. The 

 anterior fissure is wider and better marked. In it run both 

 layers of the pia mater. The posterior fissure appears as a 

 septum due to the prolongation of the inner layer of the pia mater 

 into it, the outer layer of the pia runs over the fissure. The 



