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Concentration of Photogenin and Photophelein in Cypridina

light, water, mm, visible and reaction


In the normal secretion of

Cypridina there is more photogenin than photophelein, as may be seen by adding fresh photophelein to the normal secretion after the light has disappeared on standing. The light again appears. The photophelein had been completely used up. This may be shown in another way by allowing a concentrated mixture of photogenin and photophelein to stand until the light disappears, and then boiling one-half of the mixture. Upon mixing the two halves no light as all the photophelein had been used up before the photo genin destroyed in the tube boiled.

The concentrations of the two substances which will give visible light when mixed are very Mall. In one experiment performed 15 min utes' after the photophelein was obtained, 1 Cypridina in 25,600 c.c. of water gave a just-visible light when mixed with an equal volume of more concentrated photogenin. The photogenin from 1 Cypridina in 25,600 c.c. of water will also just give visible light when mixed with an equal volume of more concentrated photophelein.

We can see how small an amount of photogenin will give light when we consider that the animal is about 3.5 by 2.5 by 1.5 mm. and that the luminous gland is more or less of a cylinder 0.64 mm. high by 0.24 mm. diameter, with a volume of about 0.03 mm. or 0.00003 cm. and that 1 luminous gland in 25,600 c.c. water will give visible light when mixed with an equal volume of photophelein, or in a concentra tion of 51,200 c.c. Hence 1 part of gland in about 1,700,000,000 parts of water will give visible light upon the addition of photophelein.

Even this is a low estimate, as we do not know what the concentration of the photogenin is in the gland itself.

When we compare the amount of photogenin which can be detected by light-production with the amount of substances detectable by chem ical means, we see how extraordinarily sensitive the light-reaction is. AgC1 is soluble in water to the extent of 1 part in 625,000 parts water at 20° (14), so that more chloride than this must be present to be detected by AgNOz, a very delicate reaction. KMnO4 is roughly just distinguishable by its color in a 14 mm. test-tube in a concentration of 1 to 1,250,000.

Biological reactions are, generally speaking, more delicate than inorganic reactions. Zinc in traces has a favorable influence on the growth of molds and 1 to 25,000,000 will increase the weight of a crop of Aspergillus by 50 per cent (la). Copper will kill Spirogyra in 1 minute when present in 1 to 77,000,000 concentration (is). Accord ing to Kastle (is), blood in 1 to 80,000,000 can be recognized by the phenolphthalein reaction. Since this reaction is due to hemoglobin, of which blood contains about 10 per cent, the hemoglobin can be recognized in 1 to 800,000,000 concentration. These figures give an idea of the delicacy of the photogenin-photophelein reaction as com pared with others. It should be borne in mind that pyrogallol in 1 to 254,000 will give visible light with potato-juice and (see p. 225).