1. Lymphoid cells from rat and human fetal livers and adult rat lymph nodes were studied by means of various cytologic, cytochemical and optical technics.
2. Freshly dried smears preserve cytoplasmic detail with an extraordinary degree of accuracy.
3. Mitochondria, both numerous and pleomorphic, are preserved in the cytoplasm which lies beyond the nuclear membrane as well as in the thin layers of cytoplasm above and beneath the nucleus.
4. In dry-fixed preparations stained with Romanowsky dyes, mitochondria appear as negative images (light areas) in basophilic cytoplasm. These negative images within the nuclear area contribute to the formation of what hematologists in the past have described as parachromatin.
5. The dry smear method of studying lymphoid blood cells produces nuclear patterns formed by the sum total of nuclear and cytoplasmic alterations which reflect functional activity.
6. The meaning of the terms nuclear structure and nuclear pattern have been contrasted.