THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 553 



hemisphere was then cut across horizontally by Pierre Marie's coup d'election, a 

 section which passes under and just touches the extremities, anterior and posterior, 

 of the corpus callosum as it appears on the mesial aspect, and is carried horizontally 

 outwards to the lateral aspect of the hemisphere. Successive cuts were made through 

 the whole hemisphere above and below this section, and parallel to it. Each slab of 

 brain tissue averaged one and a half centimetres, and from each hemisphere alternate 

 slabs were mordanted in Midler's fluid for use with the Weigert and Marchi methods 

 for fibre-tract degeneration. Two of these mordanted slabs from each hemisphere at 

 corresponding levels were embedded in celloidin en bloc, and from the others, portions, 

 which showed sclerotic areas either recent or old, were taken through for the Weigert 

 or Marchi method. From the remaining unmordanted slabs pieces of tissue were 

 removed, either including isolated areas when these lay, e.g. in the central white 

 matter, or, when the sclerotic area involved cortex or subcortical white matter, 

 the tissue section included the adjoining convolution on one or both sides. Such 

 pieces of tissue were embedded in paraffin, or celloidin, or the combined celloidin- 

 paraffin method, or finally were cut as frozen sections. Adjoining sections were then 

 stained by as many of the available methods as possible, so that by the aid of differ- 

 ently stained sections, adjoining one another, a reconstruction of the complete 

 histological picture was made possible. 



The cerebellum, pons, and medulla oblongata were cut through by means of 

 sections parallel to the original cut, i.e. at right angles to the transverse fibres of the 

 pons, and the pieces of tissue were treated in a manner similar to that used for the 

 hemispheres, with the exception that in one or two cases the whole of these portions 

 was mordanted. 



The spinal cord was cut transversely at levels corresponding, as far as possible, 

 to the different segments. From each segment, except in the instances to be 

 mentioned later, a portion was embedded in celloidin for the Weigert myelin 

 sheath stain, a portion from each alternate segment for the Marchi method, and a 

 portion from numerous levels for paraffin embedding or frozen sections. A segment 

 from each region of the cord — -cervical, dorsal, and lumbar — was in nearly every case 

 cut longitudinally either in celloidin or paraffin sections, and in several instances, 

 when a sclerosed area was distinctly outlined on the cord surface through the pia, 

 such portions of the tissue were removed, embedded in celloidin or paraffin, and cut 

 serially either in transverse or longitudinal sections. Longitudinal sections were 

 found of special value in demonstrating changes in the myelin sheath and axis 

 cylinder. In numerous other instances sclerosed areas were traced throughout 

 their whole extent by means of serial sections, and in one case the pons and medulla 

 were cut serially and three sections in every ten stained respectively for myelin 

 sheath, axis cylinder, and cells. The smaller celloidin blocks were cut at 16m in 

 thickness ; the larger, of the whole hemisphere, varied in thickness from 24 to 36m ; 

 the paraffin sections were cut at 6m. 



