Nigrosin eosin as a stain for differentiating live and dead spermatozoa

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Abstract
1. The proportion of stained spermatozoa in a ram semen-nigrosin-eosin mixture has been found to increase with the time of exposure to the stain. Five minutes is considered to be a suitable interval for practical use. 2. The value obtained for the proportion of dead cells can be considerably affected by the selection of fields that are easy to count; fields should be chosen at random. 3. The variation between, counts on the same smear is much larger than that expected for binomial proportions. This may be due partly to the ‘clumping’ of the dead spermatozoa and partly to the difficulties of interpretation caused by the presence of many partially stained cells. 4. A significant difference was found between the estimates of the proportion dead obtained by the two experimental workers; this is thought to be due to a difference of interpretation of ‘stained’ and ‘unstained’. 5. Tables are given by which to determine the approximate accuracy of counts made on a range of numbers of spermatozoa, smears and subsamples, separate tables being necessary for ram, boar and bull semen.