1281 
mica was crossed by a radiation in a direction perpendicular 
to the cleavage plane. The photogram so obtained was much 
weaker, although the time of exposition was taken equally long, 
and although the intensity of the primary radiation was the same. 
This may be explained by observing that in the reflection the cleavage 
plane rich in molecules gives a spot, which does not appear with 
the transmitted radiation. But the other images are to be taken with 
respect to corresponding planes. The explication therefore must run 
otherwise. In both eases a cylindrical pencil with cross-section of 
about 1 mm. strikes the plate. Consequently the part struck by 
radiation of the plane richest in molecules, the reflection taking 
place under an angle « near 90°, is a good deal greater, 
1 
namely in the proportion , the number of working layers being 
cos a 
the same. In the most unfavourable case of the vector of radiation 
lying in the plane of incidence, the working vector of radiation, 
if a —= 90 —p where B is a small angle, is — S sin 29. 
The intensity of the image reflected thus will be proportional to 
I? sin? 28 (ow)? 
sin? B 
of particles pro unit of surface). For the case of the vector of 
radiation lying in the plane of incidence, sin 23 in the numerator 
is to be substituted by the unity; then the intensity will be great. 
_ As the incident pencil is not polarised, we have to expect a stronger 
effect with the reflection than with the light being directly transmitted, 
(where o is the diameter of the pencil, @ the number 
5. The reflection on rock-salt (perpendicular to a cubical axis) 
again gave a set of spots very clearly observable, situated on conical 
sections through the central spot. The spots were lying close together 
on the plate; as may be supposed they are partly to be assigned 
to different not wholly parallel layers in the crystal. 
Anatomy. — “Nerve-regeneration after the joining of a motor 
nerve to a receptive nerve.” By Prof, J. Borke. 
(Communicated in the meeting cf February 22, 1913). 
After the primary discoveries of Fontana, Monro, CRUIKSHANK, at the 
end of the 18 century, no phenomenon of life has been more 
closely studied than the process of nerve-regeneration. Attention 
was drawn to the primary degenerativn of the peripheral portion of 
a cut nerve deprived of its trophic centre, the ganglion cells (WALLER), 
and the manner after which a new nervous union was established 
