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IT lias been shown by Sandritter [17, 18] that it is possible to follow, by cytophotometric methods, the kinetics of the Feulgen reaction for deoxyribo nucleic acids (DN A). In this work, hydrolysis was performed under mild conditions (HCl at pH 1.2 and at 37°), in order to slow down the solubilization and the depurination of DN A. It was found that the lability of DN A towards progressive hydrolysis varies from cell to cell (spermatozoa, thymocytes, erythrocytes, liver cells); in particular, there is a marked différence between normal and cancer cells. This différence is ascribed by Sandritter [17, 18] to the variable proportion, in the nuclei, of eu and heterochromatin: the latter would be more résistant than the former to mild acid hydrolysis. Work along the same lines by Agrell and Bergqvist [1] who used the classical conditions of acid hydrolysis (1 A' HCl, 60°) for the Feulgen reaction has suggesled that nuclei from young embryonic stages and from differentiated cells give différent hydrolysis curves. We recently undertook [6] work of similar nature, using still milder condi tions of hydrolysis (HCl 1 A' at rooni température for 1 to 8 days); our main purpose was to compare embryonic to adult cells, as had been done by Agrell and Bergqvist [1 ]. The advantage of acid hydrolysis at low température is that the dégradation which follows the loss of purines is minimized [2, 8]. Our ])reliminary results have shown that différences in the kinetics of the Feulgen réaction are not spécifie of embryonic versus adult tissues; marked différences can be found among différent cells of adult organs. For instance, the DN A of the cortical lymph cells, in the liver of Xeno p us, is much more résistant to acid hydrolysis than that of parenchymatous cells or erythrocytes of the same organ. The biochemical basis for such différences-which may be important for the conlroi of cell differentiation-remains obscure; it has been suggested [4, 15, 16] that the nuclei might contain two différent kinds of DN A, with différent metabolic stabilities anci unequal résistance towards acid hydrolysis.

Actinomycin binding, which is considered as an expression of genetic activity, has been evaluated in acute and chronic cells and compared with values for both normal cells ad pathologically (infectious mononucleosis) Lymphatic leukaemia or PHA-stimulated lymphocytes, A significant increase in binding accompanies lymphocyte activation. In acute leukaemia, the binding values were well above those observed in normal cells, and differences were noted between the proliferating and non-proliferating blasts. In chronic lymphatic leukaemia, on the other hand, actinomycin binding is considerably decreased. This is taken as a sign of marked changes in genetic regulation.

SUMMARY. — The aim of this article is first to examine the space allotted to the history of science in secondary education and the training of teachers. Secondly, I analyze the response of readers to a survey on the topic undertaken by the journal L'Enseignement scientifique. In this manner is brought out the contribution of the history of science to general culture and its role in overcoming disciplinary boundaries.