602 
PHYSIOLOGY: W. E. CARREY 
Summary. — As evidence for the chemical differentiation of the cen- 
tral nervous system in invertebrates, it has been shown that, in the 
cephalopod (Loligo pealii), caffein brings about hyperirritabiUty of the 
cerebral ganglia, while camphor affects the stellar ganglia alone in the 
same sense. Atropin causes spasms in the squid, but inhibits the activity 
of the chromatophores. 
Camphor shows a selective action on the central nervous system of 
the shrimp (Crangon vulgaris) paralyzing the elements which function in 
backward swimming movements and exciting those controlling forward 
movement. 
Atropin increased the sensitivity of all the forms tested. 
1 Baglioni, S., Zs. allg. Physiol, 5, 1905, (43-65). 
2 Moore, A. R., Science, New York, N. S., 38, 1913, (131-133). 
PROOF OF THE MUSCLE TENSION THEORY OF HELIOTROPISM 
By Walter E. Carrey 
PHYSIOLOGICAL LABORATORY OF TULANE UNIVERSITY. AND MARINE BIOLOGICAL 
LABORATORY. WOODS HOLE 
Communicated by J. Loeb, September 13, 1917 
That the mechanism by which heliotropic organisms are oriented to 
light should be identical with that for the orientation to the galvanic cur- 
rent was demanded by the tropism theory developed by Loeb in 1888.^ 
The identity of the mechanism in sessile forms was early established by 
Loeb, while more recently Bancroft^ has clearly shown that the tenets 
of the theory hold also in the movements of Euglena, which are accom- 
plished in an identical way whether under the influence of light or of the 
constant current. 
It is the aim of this paper to show that the movements of many helio- 
tropic insects under the influence of light are to be explained as forced 
motions due to the effects of light upon the tension or tonus of the 
muscles and that in this regard, there exists an exact analogy to the 
effects of the constant current in the animals investigated. 
Loeb and MaxwelP showed that when a constant current passed 
from side to side of Palcemonetes the legs on the anodal side were flexed, 
while those on the cathodal side were extended. With the anode at the 
anterior end the anterior legs were flexed and the posterior extended. 
Reversal of the current reversed the condition of tension in these legs 
and body changes were also induced. The whole response persisted 
while the current flowed and put the animals in such a condition that 
any movement forced them toward the anode. Similarly it was shown 
