384 Journal of Coiiiparalk'e Neurology and Psychology. 



Operative Technique. 



Through the occipital portion of the corpus callosum in 

 rats of various ages (0.5, 3, 7, 21, 30, 40, 60, 70 daj's old), an 

 incision was made in the left cerebral hemisphere about one milli- 

 meter to the left of the great longitudinal sinus and two millimeters 

 frontal to the lateral sinus, in such a way that a wound one and 

 a half millimeters long and two or three millimeters deep was 

 made in the posterior part of the occipital lobe, parallel to the 

 midplane. The animals were killed forty-five days after the 

 operation. In each case serial frontal sections through the left 

 occipital lobe were prepared according to the Pal VVeigert 

 technique. 



Results. 



In so simple an operation asepsis is not difficult to obtain. 

 The wounds were covered with collodion and remained well pro- 

 tected until healing had taken place. The animals recovered 

 rapidly and after twent}'-fom- hours appeared to be perfectly 

 normal. During the entire subsequent period they were in ex- 

 cellent physical condition, and equaled in weight the rats of the 

 same age in the laborat(M-y. In only one case did the post- 

 mortem examination show any trace of inflammatory reaction. 

 In this rat slight adhesions were present between the dura and 

 the brain scar, but these produced no appreciable effect on the 

 results. 



The mildest form of the cellulipetal degeneration is found 

 in the brain of the oldest rat (seventy days old at the time of 

 operation). Except for the comparatively narrow band of scar 

 tissue, there is no area in which complete degeneration of all 

 the fibers has taken place. Portions of many fibers must have 

 been cut off from their cells of origin, and these portions have 

 no doubt undergone complete Wallerian degeneration, al- 

 though the debris resulting from their disintegration has been 

 entirely absorbed. Thus on each side of the cicatrix there is 

 brain tissue which at first sight appears normal. But on closer 

 examination man)' of the fibers in the immediate vicinit}' of the 

 scar are found to differ from the normal in that they have an 



