106 General Notes. [January, 
exaltation of a heat-responding nerve into one capable of vibra- 
ting in harmony with the shorter waves of light. In the Euglena 
viridis a colorless and transparent area of protoplasm lies in front 
of the pigment spot, and is the point most sensitive to light. 
Progressingupward we ever meet with the same arrangement, 
transparency immediately in front of the part to be exalted, and 
pigment immediately behind it. 
Nature has made the most of her two factors by exposing 
the selected tissue to the continued impinging of waves of light, 
at the same time securing not only the transmission through it of 
the waves of heat, but their constant accumulation behind it, 
thereby causing the molecular constituents of the protoplasm to 
be thrown into the highest rates of vibration possible with the 
means at disposal. 
Recognizing the effects of simultaneous light and heat when 
their influence is concentrated, by a local peculiarity, on a partic- 
ular part, must it not be evident that in an individual unprotected 
by hair and unscreened by clothes, living beneath the vertical 
rays of an equatorial sun, the action of these two forces playing 
through a transparent skin upon the nerve endings over the entire 
surface of the body, must be productive of intense, but at the 
same time disadvantageous nerve vibrations, and that presumably 
such individuals as were least subject thereto would he best 
adapted to the surroundings. Nature having learned in ages past 
that pigment placed behind a transparent nerve will exalt its 
vibrations to the highest pitch, now proceeds upon the converse 
reasoning, and placing the pigment in front of the endangered 
nerve reduces its vibrations by so much as the interrupted light 
would have excited, a quantity which, though apparently trifling, 
would, when multiplied by the whole area of the body surface, 
represent a total of nervous action that if continued would soon 
exhaust the individual and degrade the species. 
Thus it is that man still retains in its full strength the color of 
skin which, while it aided him materially in his early escape 
from his enemies, is now continued because it has a more im- 
portant office to fulfill in warding off the millions 6f vibrations a 
second which would otherwise be poured in an uninterrupted 
stream upon his exposed nervous systen.—Nature, Aug. 21,84. 
MICROSCOPY. 
Mopern Metuops oF Microscoricat REsEARCH.—Microscop- 
ical technique has made such rapid progress in the last few years 
that it has been found necessary to supplement our hand-books of 
methods through the publication of special journals and depart- 
ments of journals which undertake to bring together the latest 
discoveries and improvements. A new and very important line of 
1 Edited by Dr. C. O. WHITMAN, Mus. Comparative Zoology, Cambridge, Mass. 
