398 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
group, thus confirming von Lenhossek’s discovery of centrosome and 
sphere in the same calls. 
He suggests, as an explanation of certain discrepancies, that there 
are two kinds of sympathetic ganglion-cells : — (1) those surrounded by 
spiral fibres, giving off a single undivided nerve-process to the peri- 
phery, and corresponding to the motor cells in the anterior cornu of the 
spinal cord ; and (2) those without the spiral fibres, and with a process 
which divides into a half going central wards and a half going to the peri- 
phery, corresponding to the sensory nerve-cells of the cerebro-spinal 
system. 
Formation and Structure of Dental Enamel.* — Dr. J. L. Williams 
summarises the special points of the results of his research in something 
like the following terms. He has discovered the existence of a very thin 
membrane, or a structure of a membrane-like appearance, lying between 
the ameloblasts and the forming enamel. Enamel is formed by deposit 
and not by cell-calcification ; this deposit probably consists of two distinct 
cell-products. The varicosities of the enamel rods are not caused by 
acids, but represent a true structural peculiarity of this tissue. The 
varicosities correspond with the course of one set of fibres, and may 
therefore be caused by their presence. 
•y. General. 
Homology and Atavism.^ — Prof. 0. Emery emphasises the contrast 
between two kinds of variation : — (a) a variation common to a whole 
series of organs, and dependent on a germ-plasmic correlation ; and 
(6) the special differentiation of individual orgaus or groups of organs. 
He also maintains that an abnormality can be regarded as an atavism 
only when traces of the observed structure are demonstrable in the 
normal ontogeny. Deviations of which the normal ontogeny shows not 
the slightest hint cannot be referred to latent ancestral rudiments. He 
urges the distinction between retrogressive changes and reversion, 
between resemblance to ancestral structure and genuine atavism. Also, 
inter alia, he agrees with many that the succession of events in ontogeny 
is in no way the direct consequence of phylogeny, but the resultant of 
physico-chemical factors and of the relative potency of older and 
younger germinal elements. Recapitulation, palingenesis, and coeno- 
genesis, are all metaphors. 
Biological Action of Rontgen’s Rays.J — Prof. S. Capranica has 
experimented with white mice, subjecting them to the action of Ront- 
gen’s rays. In his introductory experiments he found that the same 
quantity of C0 2 was given off in complete darkness and in diffuse day- 
light, but that intense illumination, whether solar or artificial, had a 
marked effect on respiration. Rontgen’s rays had no influence on the 
amount of C0 2 eliminated, either during digestion or during fasting. 
But they were followed by a marked nervous excitement, in regard to 
which details arc promised. 
* Proc. Roy. Soc. Lond., lix. (1896) pp. 181 and 2. 
+ Biol. Centralbl. , xvi. (1896) pp. 344-52. 
X Atti ft. Accad. Lincei (Rend.), v. (1896) pp. 416-7. 
