A series of measurements was made of the diameters of the cells and nuclei of the primary spermatocytes of the snail Helix aspersa in preparations made by embedding in paraffin wax after fixation in a number of different cytological fixatives. These were compared with similar measurements made on the living spermatocytes mounted in suitable saline solutions, and the shrinkage that the cells underwent as a result of fixation and embedding in each case was calculated from the medians of the size-distributions recorded.

The results showed that the amount of shrinkage varies to some extent according to the fixative employed--picric acid gave the greatest linear cell-shrinkage (about 40 per cent.) and Sanfelice's fluid by far the least (about 13 per cent.); but with this one exception the differences in final cell-size were not very great, and represent a linear shrinkage to about 67 per cent, and a volume shrinkage to about 30 per cent, of the original dimensions of both cell and nucleus.

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