11. ORGANISMS AND THERMAL ENERGY
497
time, k a constant depending on the shape of the animal, G the body
weight, and n an exponent which varies from 0.75-0.82, has been found
to hold by several investigators (55, 56, 57). If the differences in
metabolic intensity were purely to compensate for differences in heat
loss due to differences in surface /volume ratio, as was originally postulated by Rubner (58), then the value of n would be 0.67. The higher
values of n indicate a more complex relationship than that predicted by
the surface rule.
Discussion of the various structures developed for insulation and
heat exchange by homoiotherms, or of the nervous and hormonal factors
involved in temperature control, would involve a major digression into
mammalian physiology and lead far from the field of biochemical responses to thermal energy (cf. Hensel, 12, for example, for discussions of
these subjects). Here, it will suffice to mention that temperature control appears to be one of the more advanced and delicate functions of
homoiotherms, and one which can at times be lost temporarily, e.g., in
hibernating animals, or in cats under deep narcosis (37).
III. Organisms with Unusual Thermal Requirements
A. CRYOPHILS
The ability to live at extremely low temperatures, often below the
freezing point of water, is found among a number of plants, microorganisms, and poikilothermic animals (homoiothermic organisms living at subzero temperatures pose a problem in insulation and heat
exchange rather than biochemistry). Siberian larches survive temperatures as low as —67.8° (12). Several herbaceous plants can carry out
photosynthesis at —2 to —3°, and respiration at —6 to—7° (59). Algae
in polar seas live at even lower temperatures (60). Some insects can
survive at —20 to —30° (61), and are found active at as low as —6° in
snow and glacial ice (62). Various bacteria are notable for their ability
to metabolize and develop at subzero temperatures in media such as
foodstuffs, where freezing is prevented. To cite some examples, members
of the Fseudomonas group were isolated from glacier water by Schmelz
in 1888 (63). In the same year Fischer (64) isolated cryophilic representatives of various bacteria from sea water, soil, and foods. Bacteria
will grow in ice cream at as low as —10° (65). Horowitz-Wlassowa and
Grinberg (66) observed among microbes capable of growth at —4 to —7°
various cocci, spore-forming rods, a few yeasts, and many molds. The
multiplication of these microorganisms was very slow at the subzero
temperatures; many of them had optimal temperatures around 37°. Conn
(67) found that freezing temperatures in soil still permitted extensive
bacterial development.
497
time, k a constant depending on the shape of the animal, G the body
weight, and n an exponent which varies from 0.75-0.82, has been found
to hold by several investigators (55, 56, 57). If the differences in
metabolic intensity were purely to compensate for differences in heat
loss due to differences in surface /volume ratio, as was originally postulated by Rubner (58), then the value of n would be 0.67. The higher
values of n indicate a more complex relationship than that predicted by
the surface rule.
Discussion of the various structures developed for insulation and
heat exchange by homoiotherms, or of the nervous and hormonal factors
involved in temperature control, would involve a major digression into
mammalian physiology and lead far from the field of biochemical responses to thermal energy (cf. Hensel, 12, for example, for discussions of
these subjects). Here, it will suffice to mention that temperature control appears to be one of the more advanced and delicate functions of
homoiotherms, and one which can at times be lost temporarily, e.g., in
hibernating animals, or in cats under deep narcosis (37).
III. Organisms with Unusual Thermal Requirements
A. CRYOPHILS
The ability to live at extremely low temperatures, often below the
freezing point of water, is found among a number of plants, microorganisms, and poikilothermic animals (homoiothermic organisms living at subzero temperatures pose a problem in insulation and heat
exchange rather than biochemistry). Siberian larches survive temperatures as low as —67.8° (12). Several herbaceous plants can carry out
photosynthesis at —2 to —3°, and respiration at —6 to—7° (59). Algae
in polar seas live at even lower temperatures (60). Some insects can
survive at —20 to —30° (61), and are found active at as low as —6° in
snow and glacial ice (62). Various bacteria are notable for their ability
to metabolize and develop at subzero temperatures in media such as
foodstuffs, where freezing is prevented. To cite some examples, members
of the Fseudomonas group were isolated from glacier water by Schmelz
in 1888 (63). In the same year Fischer (64) isolated cryophilic representatives of various bacteria from sea water, soil, and foods. Bacteria
will grow in ice cream at as low as —10° (65). Horowitz-Wlassowa and
Grinberg (66) observed among microbes capable of growth at —4 to —7°
various cocci, spore-forming rods, a few yeasts, and many molds. The
multiplication of these microorganisms was very slow at the subzero
temperatures; many of them had optimal temperatures around 37°. Conn
(67) found that freezing temperatures in soil still permitted extensive
bacterial development.