The intensity of mitogenetic radiation was estimated from data given by Gurwitsch.

The sensitivity of the biological method and of the physical methods were compared.

With onion-base pulp and onion roots as mitogenetic inductors, the photographic method gave no perceptible blackening for exposures up to 184 hours.

A photoelectric counter tube was described with cadmium as photoelectric metal. Its sensitivity was such that a radiation intensity of 10 to 15 quanta per cm.2 per second of the Hg line 2536 A was detectable.

Spurious effects produced by the counter tube were described and means for their avoidance given.

A number of different biological materials, all supposed to be excellent mitogenetic radiators, were investigated by means of the counter tube. No mitogenetic radiation could be detected.

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