. Les contributions du Laboratoire de Botanique, vol 11. La botanique, la botanique. MICEPTACLL MITOGENLTIC QUARTZ RADIATEUR POUR TOAMPUFIER.HAUT-PARLEUR MAGNÉTOPHONE ET TRANbPARENT0OV5 VIN QUARTZ COLLECTEUR DE CONDENSATION, PHOTOCLECTRIC SURFACE ACTIVE. SURrACE. TOACCELERATING POTENTIAU. Fig. 106.- Deux types de compteur Geiger-Müller-tubes pour mesurer les rayons Gurwitsch. (À partir de Glasser et Seitz.) de l'œuvre par le simple fait que les deux cultures de levure, traités et de contrôle, dans la mesure de l'hématocrite (capillaires), pile à différentes hauteurs. Qu'une augmentation du nombre de cellules résultats de l'exposition à l'Gurwit

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. Contributions from the Botanical Laboratory, vol. 11. Botany; Botany. QUARTZ MICEPTACLL FOR MITOGENLTIC RADIATOR TOAMPUFIER.LOUD SPEAKER AND TAPE RECORDER TRANbPARENT QUARTZ VIN0OV5 CONDENSING COLLECTOR SURFACE, PHOTOCLECTRIC ACTIVE. SURrACE. TOACCELERATING POTENTIAU. Fig. 106.— Two types of Geiger-Mueller counter-tubes for measuring Gurwitsch rays. (From Glasser and Seitz.) of the work by the simple fact that the two yeast cultures, treated and con- trol, in the measuring (hematocrit) capillaries, pile up to different heights. That an increase in cell number results from exposure to Gurwitsch rays can, in the face of such evidence, hardly be questioned. The experiments so far cited have all had to do with living material, both sender and receptor being growing cells. We can now proceed to a considera- tion of physical means of detecting, and physical and chemical means of producing the rays. The earliest attempts to produce a non-living detector in- volved the photographic plate. If the Gurwitsch rays are of the nature of ultra-violet light, they should readily affect a photographic plate. Reiter and Gabor (43) thought that they had observed such an effect, but Gurwitsch believes that the photographic plate is not a sufficiently sensitive detector of the rays. The photographic plate is particularly sensitive to ultra-violet light and is accumulative in its action, as attested to by the long astronomic ex- posures made of invisible stars. The photographic plate should, therefore, be especially well suited as a detector of the Gurwitsch rays, but so far this has not proved to be true. The difficulty possibly lies in the fact that tissues radiate only at definite periods in their life rhythm. If light is emitted periodically from a very weak source, the accumulative action on the photo- i graphic plate may be insufficient to record it, while a more sensitive detector may catch one flash. There is also the fact that certain sources of rays, in particular yeast, re

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