306 % PHYSIOLOGY CHAP. 



exclusively, since they never occur except in the brain of persons 

 suffering from physiological decrepitude or in whom abnormally 

 early decrepitude has caused a particular form of disease called 

 senile dementia. Of these changes the first to be mentioned are 

 Kedlich-Fischer's miliary necroses or senile spots, extremely 

 small areas of destruction scattered sometimes in very large 

 numbers all over the cerebral cortex (Figs. 123, 124). The 

 majority of the remaining nerve cells are found to be in a more 

 or less advanced state of fatty degeneration (Figs. 126 a, b, c, 125 6), 

 and in these cells a special form of change is often noticed in the 

 neuro-fibrils, which are wound round and round in bundles as 

 in a ball of thread. Many cells besides succumb to simple atrophy, 

 advanced rarefaction of the spindles of Nissl (Fig. 125 c) and 

 to 'sclerosis (Fig. 125 d). The nerve fibres probably diminish 

 in number ; the radiating and transverse fibres appear to be 

 rarefied in the white and grey matter of the convolutions. The 

 atrophy of the medullary sheaths shows us why the atrophy of the 

 white substance seems greater than that of the grey matter. We 

 also find in the senile brain sclerotic retraction of the neuroglia, 

 in which accumulations of fatty granules are also found. 



Cerletti has recently described loops, knots, and extremely 

 complicated tangles in the blood-vessels of the grey matter, 

 formed by one or more small arteries, pre-capillaries, and veins 

 (Fig. 127). These strange formations, which are constantly found 

 in the senile brain, are due partly to atrophy of the tissue 

 traversed by the vessels, partly to their gradual distension owing 

 to the decreasing resistance offered by their walls to internal 

 pressure. Since many vessels are not affected by the atrophic 

 processes which attack the nervous parenchyma, they are forced 

 to adapt themselves to a course much shorter than their length ; 

 they therefore pursue a tortuous path which in its later stages 

 causes the formation of loops and extremely complicated figures 

 (Fig. 127 6). 



The presence of innumerable miliary necroses, the various 

 trophic and degenerative changes in the cells and nerve fibres, 

 the sclerotic retraction of the neuroglia, and the alterations in the 

 parenchyma consequent on the disturbances of nutrition caused 

 by the winding course of the blood-vessels result in serious atrophy 

 of the brain as a whole. It shrinks, and its absolute weight 

 diminishes (1295-1095 grms. according to Verga) ; the con- 

 volutions become thinner and the sulci wider. This atrophy is 

 prevalent in the frontal lobes, the corpus callosum, the corona 

 radiata, and the grey nuclei of the base ; it results in an ex vacuo 

 dilatation of the ventricular cavities. These changes are not equally 

 marked and constant in old people of the same age, but take place 

 very early in some and late in others. Hansemann found that 

 the brains of Mommsen and Bunsen, who died at 86 and 



