Tem-perature: Metabolic Aspects and Perception 35 1 



with lateral line neuromasts. They show autonomous rhythmic activity which 

 initially increases on cooling and decreases on warming.'"'- They respond to 

 a difference of half a degree in the range of 10 to 15°; after the initial response 

 to cold or warmth they adapt, and the equilibrium level of activity varies 

 directly with temperature. The role in behavior of the lateral line responses in 

 bony fish and the ampullar response in elasmobranchs is not clear. 



When warm or cold water is squirted against the flank of a bony fish the tail 

 fin gives a characteristic turning response. This stops after the spinal cord has 

 been transected between the region of stimulus and response but not after 

 the lateral line nerve has been cut.^- Hence the sense organs must be in the 

 skin. Impulses have not been recorded in spinal nerves in response to thermal 

 cutaneous stimulation, '"''' but they may well be in such small fibers that asyn- 

 chronous spikes would be below the sensitivity of an amplifier. Fish of several 

 sorts were trained to give a feeding reaction to warming, and this response 

 persisted after cutting of the lateral line nerves.^- It is probable that assump- 

 tion of a position in a temperature gradient is also dependent on cutaneous 

 thermal receptors. Such receptors have not been localized in Hsh. 



By a combination of temperature receptors, partly lateral line organs, am- 

 pullae of Lorenzini, but principally cutaneous thermal receptors, Hsh are 

 stimulated by heat and cold to selective orientation reactions. Whether there 

 are any vasomotor reactions as well is not known. 



Poikilotherms Inhabiting Moist Air: Body Temperature. In air, loss of heat 

 by conduction is less important than in water, but loss by radiation and con- 

 vection and loss by vaporization of water are more important. For each gram 

 of water evaporated (at 33°) 580 gram calories of heat are absorbed by the 

 water, and the surface is thereby cooled. In sunlight, absorption of radiant heat 

 from the sun may be important, but this warming mechanism is seldom of 

 significance under water. • 



Cooling by vaporization depends on the vapor tension and air currents in 

 the vicinity of the organism. The temperature of a- slug or of an extended 

 Helix, for example, is well below that of the surrounding air as measured by 

 a dry-bulb thermometer unless the air is fully saturated. However, if the air 

 temperature is measured with a wet-bulb thermometer, the slug is at the air 

 temperature. When-^:?e[ix withdraws into its shell it is protected against 

 evaporation. ''^' The temperature of an earthworm in dry air soon diverges 

 above the wet-bulb temperature, owing to rapid surface drying,"^" but in water 

 the temperature in the intestine rapidly adjusts to the environmental tempera- 

 ture.^'^-- "' It is difficult to compare body temperature with air temperature. 

 Few animals have continuous surface evaporation, as from a wet-bulb ther- 

 mometer, yet all have some evaporation. Hence, where there is no active 

 temperature regulation, the body temperature must be lower than a dry-bulb 

 and may be higher than a wet-bulb temperature. Active physiological regula- 

 tion can be demonstrated onK' if physical cooling by vaporization is eliminated 

 bv measuring body temperature against a thermometer from which there is 

 equal \'aporization, or in a saturated atmosphere. If measurements are made 

 in sunlight, absorption of radiant heat must be considered. 



The temperature relations of Amphibia are closely related to their water 

 balance.-' '^- ^"'^^ ^-•^ Frogs lose water in proportion to the relative humidity; 

 but thev are unable to absorb water even from saturated air, because their 



