1883.] Physiology. 441 
second the electrical relations of the two surfaces of the leaf are 
reversed, the lower surface becoming now positive to the upper. 
“A voltaic current directed from the upper to the under sur- 
face, which is too weak to invoke an excitatory res e, pro- 
duces an increase of the positivity of the under surface, limited to 
the part of the lobe through which the current passes, which lasts 
several seconds after the current is broken. * * * Whena 
leaf is subjected to series of inadequate induction shocks at short 
intervals (e. g., one-twentieth of a second), the response may occur 
after a greater or less number of excitations, according to the tem- 
perature at which the experiment is made and the strength of the 
current. * * * Tna series of mechanical excitations, each of 
which is just adequate to produce an electrical response, those 
which occur earliest are followed by no change of form. Of the 
later members of the series each produces a measureable move- 
ment, the extent of which becomes greater each time that the 
excitation is repeated until eventually the leaf closes.” 
he first electrical change which the leaf of Dionza undergoes 
after excitation (the increased negativity of the under surface of 
the leaf) is probably a physiological change which is the outcome 
of some functional explosion in the cell protoplasm, and is closely 
analogous to the “action current” which is a sign of functional 
excitement in an animal nerve or muscle. The second electrical 
condition, which is more slowly brought about and is more lasting, 
in which the under surface of the leaf becomes positive to the 
upper, is probably due simply to the transference of water from 
the cells to the intercellular spaces. 
THE INFLUENCES WHICH DETERMINE SEX IN THE EMBrvo.—Pro- 
sor E. Pflüger publishes at length an account of experiments, 
<tiormed with the greatest care, with the object of throwing 
light upon some of the most prominent of the obscure problems 
of the physiology of generation (Pfliger’s Archiv., Bd. XXIX, 
Heft 1 and 2). Professor Pflüger made use of frogs in his experi- 
; Many hundreds of the creatures were obtained from vari- 
Sus neighborhoods, and were maintained while under observation 
under conditions made as nearly normal as possible. 
irst question attacked is: Does the concentration of the 
spermatic fluid of the male influence the sex of the offspring ? 
Much care is necessary in handling frogs’ eggs, for they are ex- 
eee Susceptible of mechanical injury. The pair of frogs are 
