Part 3 (1/2)
6. Oxidation in acid permanganate. (Pyrogallol.)
7. Oxidation in persulfates and perborates. (Formaldehyde, paraformaldehyde.)
8. Oxidation in perchlorates, periodates, and perbromates. (Palmitic acid.)
9. Combination of 2 and 4. (Many organic substances.)
10. Combination of 3 and 4. (Many organic substances.)
11. Oxidation with H_{2}O_{2} and haemoglobin or vegetable oxidases.
(Pyrogallol, gallic acid, lophin, esculin.)
12. Oxidation with H_{2}O_{2} and MnO_{2}, Fe_{2}Fe(CN)_{6} Mn(OH)_{2} + Mn(OH)_{3} Ag_{2}O, chromium oxide, cobalt oxide. (Pyrogallol.)
13. Oxidation with H_{2}O_{2} and ferrocyanides, chromates, b.i.+.c.hromates, permanganates, Fe salts, and Cr salts. (Pyrogallol, esculin.)
14. Oxidation with H_{2}O_{2} and collodial Ag. Pt. Pd. Au.
(Pyrogallol.)
The spectrum of chemiluminescent reactions has been described in a few instances as continuous but no definite measurements of its extent have been made. Radziszewski (1880) found the light of lophin oxidized in alcoholic caustic alkali, examined with a two-prism spectroscope, to give a continuous spectrum, brightest at _E_, with the red and violet ends lacking. Trautz (1905, p. 101) states that the pyrogallol-formaldehyde-Na_{2}CO_{3}-H_{2}O_{2} reaction gives a continuous spectrum from the red to the blue green with maximum brightness in the orange. Weiser (1918 _a_) has studied the spectra of some chemiluminescent reactions by photographing the light behind a series of color screens. He finds also that the spectra are short, with maximum intensity in various regions. Thus, _amarin_ oxidized by chlorine or bromine, extends from the yellow to greenish blue with a maximum in the green while _phosphorus_, dissolved in glacial acetic acid and oxidized with H_{2}O_{2}, luminesces from yellow green to violet.
The spectra of luminous animals are quite similar to those of chemiluminescent reactions. Moreover, as we have seen, chemiluminescence is essentially an oxyluminescence, since oxygen is necessary for the reaction. All luminous animals also require oxygen for light production.
Therefore, bioluminescence and chemiluminescence are similar phenomena and they differ from all the other forms of luminescence which we have considered. The light from luminous animals is due to the oxidation of some substance produced in their cells, and when we can write the structural formula of this photogenic substance and tell how the oxidation proceeds, the problem of light production in animals will be solved.
CHAPTER III
PHYSICAL NATURE OF ANIMAL LIGHT
Interest in the light of animals from a physical standpoint has centred around questions of quality, efficiency and intensity, but in only one group of luminous animals, the beetles, have accurate measurements of these characteristics been made. This is due in part to the abundance of these forms and their appeal to human interest and in part because they are among the brightest of luminous organisms. Weak lights are not only difficult to measure but, when dispersed to form spectra, give bands so faint that their limits are very difficult to see and more so to photograph. Very few organisms produce light visible to the fully light-adapted eye. Although their light may seem quite bright to the dark-adapted eye, the dark-adapted eye is a poor judge of the quality, _i.e._, the color of a light. This is because of the Purkinje phenomenon, a change in the region of maximum sensibility of the retina with change in intensity of the light. For an equal energy spectrum, to the normal, completely light-adapted eye, yellow-green light of wave-length, ? = .565, appears the brightest, but when the light is made fainter the maximum s.h.i.+fts first to the green and then to the blue.
The dark-adapted eye can see green or blue better than yellow and for this reason weak lights will appear more green or blue than stronger ones of the same energy distribution. Also two weak lights of the same spectral composition may appear different in color if they differ much in intensity. This is ill.u.s.trated in Fig. 6.
[Ill.u.s.tration: FIG. 6.--Visibility curves for three illuminations showing the s.h.i.+ft in region of maximum visibility, or Purkinje phenomenon (_after Nutting_).]
The s.h.i.+ft in sensibility of the eye occurs in illuminations of between 0.5 and 50 metre-candles and represents a change from central cone vision (high intensities) to peripheral rod vision (low intensities).
The _fovea centralis_ lacks rods and this part of the eye becomes practically color blind at very low intensities of light. Below 0.5 and above 50 metre-candles visibility varies but little with change in intensity. It is clearly necessary then to distinguish between the physical objective phenomenon of light and the physiological subjective sensation of light.
It is a fact that different luminous animals produce light of quite different colors as judged by our eye. A range of spectral tints has been described which extends from red to violet but ”yellowish,”
”greenish” and ”bluish” tints are commonest. Indeed one or two animals possess several luminous organs emitting lights of different colors.
This is true in a South American firefly, _PhenG.o.des_, whose lights are red and greenish yellow, and in the deep sea squid, _Thaumatolampas diadema_, which produces lights of three colors, two shades of blue and red. The red light in the case of the squid appears to be due to a red color screen formed by the chromatoph.o.r.es, but in _PhenG.o.des_ no screen is present.
TABLE 4
_Wave-lengths of Fraunhofer Lines and Prominent Lines in Line Spectra_
FRAUNHOFER LINES
======================================================================== Line
Color
Wave-lengths
Source
( = /1000)
------------------+------+---------------------+------------------------ A
Red
759.4 (band)
Oxygen in atmosphere.
a
Red
718.5 (band)
Water vapor atmosphere.
B
Red
686.7
Oxygen vapor atmosphere.
C
Red
656.3
Hydrogen in sun.
D_{1} D_{2}
Yellow
589.6, 589.0
Sodium in sun.
E
Green
527.0
Calcium in sun.
b_{1} b_{2} b_{4}
Green
518.4, 517.3, 516.8
Magnesium in sun.
F
Blue
486.1
Hydrogen in sun.
G
Violet
430.8
Calcium in sun.
H K
Violet
396.9, 393.4
Calcium in sun.
BUNSEN FLAME LINES
=============================================== Source
Color
Wave-lengths ( = /1000) ----------+--------+--------------------------- Pota.s.sium
Red
769.9, 766.5 (double) Lithium
Red
670.8 Sodium
Yellow
589.6, 589.0 (double) Thallium
Green
535.1 Magnesium
Green
518.4 Strontium
Blue
460.7 ----------+--------+---------------------------
PLuCKER TUBE LINES
=============================================== Source
Color
Wave-lengths ( = /1000) ----------+--------+--------------------------- Mercury
Yellow
579.0, 576.9
Green
546.1
Blue
491.6, 435.8
Violet
407.8, 404.7 Hydrogen
Red
656.3
Blue
486.1, 434.1 Helium
Red
728.2, 706.5, 667.8
Yellow
587.6