ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
583 
that a substantial selective death-rate actually exists at work on~man- 
kind, and that, with like environment, it may amount to as much as four 
times the non-selective death-rate. In other words, natural selection 
is very sensibly effective among mankind. 
Electric Phenomena associated with Motion in Animals and 
Plants.* — Sir J. Burdon-Sanderson discussed in the Croonian lecture 
the chemical, mechanical, and electrical concomitants of muscular 
motion, with a view to the elucidation of their mutual causal relations. 
“The lecture concluded with a comparison of the electromotive pro- 
perties of the leaf of Venus’s fly-trap ( Dionsea muscipula ) with those of 
muscle. If the same method of exploration is applied to the surface 
of the leaf as to the ventricle of the heart of the frog, it is easy to show 
that the phenomena observed after excitation in the two structures are 
essentially analogous. In both an electrical change is the immediate 
result of a localised instantaneous excitation, and this change spreads 
from the excited spot to parts at a distance at a rate which varies with 
temperature. The interval of time between the culmination of the 
electrical response and that of the change of form is much more obvious 
in the leaf than in the heart, because the mechanism by which it mani- 
fests itself works very slowly, as compared even with cardiac muscular 
fibres. This contrast, however, affords no ground for doubting that the 
two processes are, as regards their intimate nature, analogous.” 
Clamping Mechanisms in Animals. f — Dr. Otto Thilo has taken 
counsel with the engineers, and has made a most interesting study of 
those mechanical arrangements, mainly of the nature of clamps, which 
are found associated with the spines of fishes, e.g. Monacanthus, Tria- 
canthus, and Gasterosteus. But he broadens his survey and interpreta- 
tion to include such adaptations as the valves of the heart and the 
erection of the viper’s fang. 
Digestion in Dogfish.J — Prof. E. Yung has made a study of the 
minute structure of the gut in Scyllium, as well as numerous physiological 
experiments on the digestive power of different regions. One main result 
stands out decisively, that the formation of pepsin is limited to a par- 
ticular region of the saccular stomach. 
A Reducing Animal Ferment. § — MM. E. Abelous and E. Gerard 
find that an extract of horse’s kidney contains a soluble ferment which 
reduces nitrate of potassium and of ammonium, decolorises metbylen-blue, 
and appears to form butyric aldehyde from butyric acid. They tried its 
effect on glucose, but without result. 
Echidnase.|| — C. Phisalix has shown that the poisonous secretion of 
Viperidae, e.g. Vipera aspis, contains a diastatic ferment (echidnase) in 
addition to the proper toxic substance. It varies in amount, according 
to the habitat and season. Thus there is more in the vipers of the 
Vendee than in those of Arbois ; there is none detectable (in the secre- 
tion) in early spring, but plenty in summer. Experiments show that 
* Nature, lx. (1899) pp. 343-6 (8 figs.). 
f Biol. Centra) bl., xix. (1899) pp. 501-17 (13 figs.). 
t Arch. Zoo). Exper., vii. (1899) pp. 121-201 (i pi.). 
’§ Comptes Rendus, cxxix. (1899) pp. 164-6. || Tom. cit., pp. 115-7. 
