Temperature: Metabolic Aspects and Perception 



TABLE 59 (contimied). 

 LETHAL TEMPERATURES OF POIKILOTHERMIC A^^LMALS 



345 



hardiness is developing/"^^' and much of the water is in a "bound" state; that 

 is, it is held by protein and is not free solvent. There is no doubt that many 

 insects freeze, in that they become soHd in cold winter weather; whether the 

 protoplasm of such cells as neurones contains ice crystals in insects with extra- 

 cellular fluid frozen is not known but seems unlikely. There are numerous 

 reports of revival of fish from a frozen state; however, the freezing must be 

 fast and superficial; true body temperatures below — 0.6 to — 1° are probably 

 not endured.-- The lower lethal temperature for fish varies within limits 

 according to the temperature to which the fish have been acclimatized. Marine 

 teleosts, which are hypotonic to the medium, and hence have a higher freezing 

 point than sea water, must approach freezing in arctic waters. 



If the rate of cooling through the temperature range of freezing is rapid, 

 about 100 degrees centigrade per second, ice crystals do not form and the 

 organism is "vitrified. "^^- When vinegar nematodes (Anguillula), slightly 

 dehydrated, are placed directly into liquid air ( — 197° C), they are solidified 

 in an amorphous state; if they are then warmed rapidly- by immersion in water 

 or mercury at 30° they revive and are active, and many survive. ^^^ If freezing 

 occurs, either by slow cooling or by slow warming from liquid air temperature 

 through the freezing temperature range to above-freezing temperature, the 

 animals are killed. Other organisms, including Protozoa and muscle cells, 

 have been vitrified. The cause of death in freezing appears to be not cessa- 

 tion of enzymatic reactions resulting from reduced thermal agitation, but 

 rather disintegration of protoplasmic organization. 



Many animals which do not become dormant or encyst die at temperatures 

 well above freezing (Table 59). Metabolism is greatly reduced, and they 

 enter a chill coma in which survival time is limited. It is probable that proto- 

 plasmic organization cannot be maintained without a certain rate of energy 

 production from metabolism. Insects go into chill coma at a lower temperature 

 if acclimatized to cold rather than warm air; Blatta orientalis, for example, 

 living at 14-17°, become inactive when cooled to 2.0° C, whereas cockroaches 

 living at 36° show no activity below 9.5° C.^^- In birds and mammals, prob- 

 ably also in large cold-blooded animals, circulatory sluggishness results in 

 insufficient oxygen to essential organs, such as the brain, and progressive 

 paralysis occurs. When heat loss exceeds heat production body temperature 

 cannot be maintained. A cat loses consciousness at a body temperature of 



