Part 4 (1/2)
Bacteria
G to F extending
Barnard,
Photographic.
toward D for
1902
long exposure
Bacteria
Somewhat beyond
Fisher,
Eye observation.
G to D
1888
Bacteria
.58 - .43
Forster,
Eye observation
1887
Zeiss. Abbe
microspectral
ocular.
Bacteria
>.500 to .350
Bright
Forsyth,
Photographic,
band
1910
quartz
at .4
spectroscope.
Agarious
0.56-0.48
Ludwig,
Eye observation, melleus
(approximately)
1884
Sorby Brown
microspectroscope.
Xylaria
.54 - .46
Ludwig,
Eye observation, hypoxylon
(approximately)
1884
Sorby Brown
microspectroscope.
Micrococcus
b into the
Ludwig,
Eye observation, Pflugeri
violet
1884
Sorby Brown
microspectroscope.
Mycelium X
.570 - .480
Molish,
Eye observation,
1904,
Zeiss comparison
book
spectroscope.
Bacterium
.570 - .450
Molish,
Eye observation, phosph.o.r.eum
1904,
Zeiss comparison
book
spectroscope.
Bacterium
.570 - .450
Molish,
Eye observation, phosph.o.r.escens
1904,
Zeiss comparison
book
spectroscope.
Bacillus
.570 - .450
Molish,
Eye observation, photogenes
1904,
Zeiss comparison
book
spectroscope.
Pseudomonas
.570 - .450
Molish,
Eye observation, lucifera
1904,
Zeiss comparison
book
spectroscope.
As first shown by Dubois (1886) for _Pyrophorus_, and confirmed by myself for _Cypridina_, the light is not polarized in any way. I may add that the _Cypridina_ light like any other light may be polarized by pa.s.sing through a Nicol prism.
Several writers [Dubois (1914 book)], Fischer (1888), Molisch (1904 book) have noticed that the light of luminous bacteria changes in color if grown on different culture media. Light which is ”silver white” on dead fish becomes ”greenish” on salt-peptone-gelatin media and more yellow on salt-poor media. Peron (1804) and Panceri (1872) describe the light of _Pyrosoma_ as yellow to greenish after death of the animal and reddish on stimulation; then fading out through orange, yellow, greenish and azure blue. Polimanti (1911) describes the normal light of _Pyrosoma_ as greenish, and states that as the animals die, or if they are kept at temperatures above the optimum, the light becomes more red.
McDermott (1911, _b_) noticed that the light of fireflies placed in liquid air became decidedly reddish just before going out and on rewarming the first light to appear was reddish followed by the proper shade at higher temperatures. I have frequently observed a more reddish color from luminous tissues of the firefly upon the addition of coagulants such as alcohol, and have noted that the light of _Cypridina_ becomes weaker and more yellow at both low (0) and high (50) temperatures. The meaning of these color changes will be discussed in Chapter VII.
The efficiency of any light may be defined in several different ways: (1) By the percentage of visible wave-lengths in the total amount of radiation emitted, _i.e._, visible radiation divided by total (heat, visible, actinic) radiation; (2) by considering, in addition to visible radiation total radiation, the sensibility of the eye to different wave-lengths, visible radiation visual sensibility total radiation.
Visible radiation visual sensibility is spoken of as luminosity; (3) by the amount of light (expressed in candles) produced in relation to a given expenditure of energy or in relation to the cost of the energy expended. Thus, of the radiation emitted from an incandescent electric lamp only a small per cent. is light, the rest being heat and actinic rays. It is therefore very far from being 100 per cent. efficient. If there were no infra-red or ultra-violet in the radiation from an incandescent lamp its efficiency would be 100 per cent. if we disregarded visual sensibility. But if we take into account the fact that the eye is most sensitive to yellow green, a source of light, even though emitting only visible radiation, would not be 100 per cent.
efficient unless its maximum of emission corresponded also with the maximum of visual sensibility. We shall return to this question in a later paragraph. Looking at the question from the standpoint of energy consumption, the carbon incandescent lamp gives one mean spherical candle for 4.83 watts (watt = 10^7 ergs per sec.), while the tungsten lamp gives one mean spherical candle for 1.6 watts, about one-third the energy, and the latter is consequently more efficient.
As we know practically nothing of the energy transformations occurring during the process of light production in organisms, all statements regarding the efficiency of their light are based on relations between the visible radiation and total radiation. This involves a measurement of rays in the infra-red region (heat rays) and ultra-violet region (actinic rays) as well as the light rays proper, and any other radiant energy produced. While all spectroscopic investigations show that the spectrum of luminous animals never extends to the limits of the visible spectrum in either the red or violet, it is possible that bands occur in the infra-red or ultra-violet, and special methods must be employed to detect these. Radiations of all kinds, if converted into heat on striking the blackened surface of a thermopile, bolometer, or radiometer can be measured by changes in temperature and the relative amounts of energy represented be compared in a common unit, the calorie. By proper screening, all rays except the visible light rays can be cut off from the measuring instrument and the amounts of energy represented in light and in total radiation thus be determined.
Dubois (1886) first studied this problem in _Pyrophorus_ by the use of a thermopile and galvanometer and found a small amount of radiation from the luminous region in excess of that from a non-luminous region. It amounted to a galvanometer deflection of 0.95 and was increased 0.3 during the flash of the insect on electrical stimulation. This increase of 0.3 is possibly due to heat produced on muscular contraction. In any case the amount of heat radiated in comparison with that of the candle is very small indeed. A more careful study has been made by Langley and Very (1890) with the bolometer. They point out first of all that the total radiation from the most powerful luminous organ (the abdominal one) of _Pyrophorus_ which affected their bolometer slightly, would, in the same time (10 seconds), be sufficient to raise the temperature of an ordinary mercurial thermometer having a bulb 1 cm. in diameter by rather less than 2.3 10^{-6} C. We may thus gain some idea of the magnitude of the measurements to be made. The radiation from _Pyrophorus_ which affected their bolometer was shown to be due merely to the ”body heat”[2] of the insect, and it is largely cut off by a plate of gla.s.s which is opaque to all wave-lengths of 3 or more. These waves are given off by bodies at temperatures below 50 C. and belong ”to quite another spectral region to that in which the invisible heat a.s.sociated with light mainly appears.” Langley and Very then compared the radiation from a non-luminous bunsen flame and the _Pyrophorus_ light, interposing a plate of gla.s.s in each case to cut off the waves longer than 3, and found several hundred times more radiation in the case of the bunsen burner but, nevertheless, perceptible radiation from _Pyrophorus_. The former consisted of radiant heat shorter than ? = 3 and extending up to the visible light rays (? = 0.7 since the bunsen flame emitted no light). The very slight effect of the _Pyrophorus_ radiation must be due to wave-lengths between ? = 3 and ? = 0.468, the limit of the _Pyrophorus_ spectrum in the blue. Langley and Very a.s.sumed it to be due entirely to the band of visible light, ? = 0.640 to ? = 0.468, and a.s.sumed that no invisible heat rays were produced. All of the energy of _Pyrophorus_ light would therefore lie in the visible region and its efficiency (light rays heat + light + actinic rays) would be 100 per cent. Later, Langley (1902) reinvestigated the radiation of _Pyrophorus_ and could detect no heating whatever with the bolometer. ”A portion of the flame of a standard sperm candle, equal in area to the bright part of the insects, gave under the same circ.u.mstances, a bolometric effect of such magnitude that had the heat of the insect been 1/80,000 as great as that from the candle, it would certainly have been recognized.”
Coblentz (1912) also, using a vacuum thermopile of Pt and Bi, was unable to detect any infra-red radiation from _Photinus pyralis_, but found that the temperature of this firefly is slightly lower than the air.
These temperature measurements will be discussed in a later chapter.
[2] Langley and Very evidently supposed that the body temperature of the firefly, like the mammal or bird, is higher than its surroundings.
The a.s.sumption of Langley and Very that the small amount of _Pyrophorus_ radiation pa.s.sing gla.s.s is all light has been called into question by Ives (1910), who points out that Langley and Very failed to use a screen which would cut off either the visible rays or the invisible rays between 3 and 0.7. They really left the question open as to whether the effect of _Pyrophorus_ light on their bolometer was due to the visible band of rays or to this plus another band in the infra-red. ”The firefly's actual efficiency as a light source is dependent to a large degree on the radiation being confined to the visible region. If there should be found infra-red of quant.i.ty comparable to the visible, the firefly, while still a very efficient source would not be, as usually supposed, the example of an ideally efficient light produced by nature.”
Ives investigated the question further by the phosphor-photographic method. ”In brief it consists of this: Phosph.o.r.escence, which is excited in various substances by exposure to short waves (blue, violet or ultra-violet), is destroyed by exposure to longer waves (orange, red, infra-red). Thus, a surface of Balmain's paint or of Sidot blende, excited to phosph.o.r.escence and then exposed in a spectrograph, will have areas of reduced brightness wherever long-wave energy has fallen upon it. If this surface is then laid on a photographic plate for a short period, a permanent record is obtained on the plate after development.”
Preliminary tests showed that the method was applicable in the case of weak light such as the firefly spectrum and also if the light is intermittent like the firefly. With Sidot blend (ZnS) the extinguis.h.i.+ng action extends from ? = 0.6 to ? = 1.5. A sheet of deep ruby gla.s.s, which cut off all the visible rays of the firefly but allowed infra-red to pa.s.s, was placed between the firefly light and a surface of phosph.o.r.escent Sidot blend which was exposed to the firefly flashes for three and a half hours. No extinction of phosph.o.r.escence occurred, while without the ruby gla.s.s, extinction, due to the orange rays of the _visible_ firefly light was noticeable in 20 minutes. There is thus no infra-red of an intensity at all comparable to the visible as far as ? = 1.5, the lower limit of the phosphor-photographic method. Coblentz (1912) had examined the transparency of the dry chitinous integument of various fireflies (Fig. 10) in the infra-red and reports it to be fairly transparent down to ? = 2.8, opaque between ? = 2.8 and ? = 3.8, transparent again to ? = 6, and opaque beyond that. The infra-red could, then, if it were emitted, largely pa.s.s through the integument which is similar in absorption properties to complex carbohydrates.
Transparency of the integument to the ultra-violet was not studied.