Methods for the Counting of Neurons

Only a short time after the neuron became identified as the essential unit of the nervous system, the first attempts were made to estimate the number of neurons in different parts of the nervous system. During the past century, a great number of methods have been used in making such estimates. Although the most widely used and accepted method is that of direct counting in the microscope, various other techniques, including photographic, projection, homogenate, automatic, and ocular methods have been designed. Brief descriptions of these techniques will be given in the following account.