The chloroplasts of three genera of marine algae, Dictyota, Padina, and Bryopsis, were labeled with tritiated-thymidine for various time periods during culture in "Erd-Schreiber's" solution. Autoradiographs were prepared from both smeared and sectioned material. They revealed that almost all of the radioactivity was in the cytoplasm and associated with the chloroplasts, as detected in the overl...

ECENTLY, the life span of the lymphocyte has become a subject of considerable interest as well as controversy among hematologists. The large numbers of lymphocytes entering the general circulation from the thoracic duct point to a short life span of less than a day,1 while isotopic experiments24 indicate either long life spans of weeks or months or reutilization of large fragments of nuclear co...

NADH-diaphorase, one of flavoenzymes, is known to lose scarcely its activity in riboflavin deficiency. In that case, as reported previously (1), the enzyme still has its activity even in the intestinal mucosa, a very actively regenerating tissue. We therefore assumed that this enzyme increased its activity directly before mitosis. In order to confirm this assumption we have studied the activity...

A factor present in homogenized normal human blood leukocytes containing alka line phosphatase activity was shown to be effective in depressing the incorporation of TDR-H3 into DNA-H* when preincubated with dog bone marrow, lymph, and human chronic granulocytic leukemia cell suspensions. Human donor blood buffy coats were extracted, and an approximately 200-fold purified preparation of leukocyt...