Abstract
1. This method of determining the actual number of Purkinje cells present in a given area of cerebellum is practicable and of sufficient accuracy to make it another useful means of studying nerve cell activity. 2. In its application to clinical cases it is found that increasing nerve cell exhaustion is accompanied by increasing nerve cell disappearance, although it is recognized that theoretically complete nerve cell exhaustion could be present without nerve cell disappearance on account of the individual dying before phagocytic action could take place. 3. This disappearance of nerve cells corroborates the theories and observations made on phagocytosis of nerve cells, inasmuch as it shows that nerve cells disappear from the brain. 4. While there are too few cases to establish a normal actual Purkinje cell count, it is of interest to note that there were 16.6 per cent. fewer cells in the case with the maximum cell exhaustion (57 per cent.) than in the case of the normal man (2 per cent.).