ae Physiology. 563 
the reflex background by means of inhibitions, the author varies 
the background as a whole thermally, and observes its effect on 
reflexes. A reflex or headless frog may be heated so slowly that 
although the heart may beat very fast, vigor caloris may be caused 
without any motor reaction of its limbs. If the heart be tied 
before hand, reflexes occur from gradual heating. This the author 
thinks explained by assuming that in the first case the hot blood 
passing inward equalizes the progressive heating throughout, or 
changes the thermal background; while in the second case, with 
no circulation, the background is fixed and the surface tempera- 
ture rises to the point of difference which causes movement.— 
Science, Vol. i, No. 5, p: 152. 
Action oF DiGITALINE ON THE CIRCULATORY OrGANS.—(Pre- 
liminary note by H. H. Donaldson and L. T. Stevens). The con- 
tinuation of the experiments begun last year has yielded the fol- 
lowing results: The work done by the heart of the common frog 
is decreased by digitaline, whatever the dose, as was previously 
shown to be the case for the heart of the “slider” terrapin. In 
both frog and terrapin, the decrease occurs, whether the aortic 
valves are intact or not. Variations in arterial or venous pres- 
sure do not affect the result. 
By a method permitting direct measurement of the fluid circu- 
lating through the viscera and lower extremities in a unit of time 
and under constant pressure, it has been determined for the frog 
that the arterioles are constricted by digitaline. On this point 
the terrapin has not yet been investigated. Digitaline has also 
shown to increase mean blood pressure in both frog and 
terrapin. We have, then, for the frog under digitaline a decrease 
in the work done by the heart, a rise of mean blood pressure, and 
a constriction of the arterioles. The first and second of these 
points have been already demonstrated for the terrapin as well.— 
Science, Vol. i, No. 5, p. 149 
PERCEPTION oF LIGHT AND COLOR BY THE LOWEST PLANTS AND 
ANIMALS.—The instances in which these faculties are exhibited 
in the lowest forms even extending to some true plants, are very 
humerous, but hitherto have met with little explanation. WwW: 
geimann suggests three principal modes by which light is able 
to affect these organisms, viz: 1. Directly, by modification of the 
interchange of gases, without apparent addition of sensation. 2. 
Y Modification of the sensation of necessity for breathing, owing 
to Modification of the interchange of gases. 3. By setting up a 
} process, which probably answers to our sensation of 
: light, ‘ Of these the first may occur either alone or in combina- 
a ton with the second; simultaneous occurrence of the first and 
third may possibly take place. 
1. Navicula is taken as the type of the first method, and most 
mobile Diatomaceze and Oscillarineæ belong to the same class. 
VOL, XVII_—wo, V, 39 
