78 A CHEMICAL SIGN OF LIFE 
these nerves are present in the body region, and they 
are wholly sensory without admixture of motor fibers. 
The fibers of both nerves are dendrites of ganglion 
cells which lie in the head. 
When these fibers were subjected to our tests it was 
found that in every case the proximal portion of the 
fresh nerve gave much less carbon dioxide than the distal 
portion, indicating that the gradient is correlated with 
function and not with development. And in this case 
it should be noted that, although the fibers of both nerves 
are dendrites of their respective neurons and conduct 
afferent impulses, the function of the two nerves is 
widely different, the lateral line nerve (ramus lateralis 
vagi) being excited by water vibration and the accessory 
lateral line nerve (ramus lateralis accessorius) being 
exclusively gustatory in function. The quantitative 
estimates on these nerves given in Table XII will illus- 
trate the presence of this marked gradient of carbon 
dioxide of the sensory dendrites. 
TABLE XII 
CarRBON DIOXIDE PRODUCTION FROM DIFFERENT PORTIONS 
oF LaTEeRAL Line NERVE (Ramus LATERALIS 
VaGI) OF CARP 
Amount of CO: 
Portions of |Temperature Given Off by 10 mg. 
Nerve Degrees C. of the Nerve in 
ro Minutes 
Proximal...... 24 4 9X1077- 5.2X107 7g. 
Distal......... 24 12.4X107/7-18.5X10—7g. 
That the metabolic gradient is directly associated 
with the functional direction is strikingly shown also by 
further studies with different fibers in which quantitative 
determinations were not made, but in which the output 
