It is hardly worth inquiring into the nature of the substances in each particular extract which may for convenience be collectively spoken of as photophelein, since I have found a great many simple bodies which, mixed with concentrated photogenin in powder or crystal form, give rise to a bright light. With more dilute solutions (one Cypridina to 10 c.c.) no light appears. These substances include sodium glyco cholate, sodium taurocholate, thymol, chloroform, hydrochinon, NaC1, butyl alcohol, saponin, oleic acid, ether, benzol, atropin, pilocarpin, and ortol. Chloral hydrate, pyrocatechin, (N114)2SO4, esculin, dextrine, and gave a fainter light, while saccharose gave none.
It is difficult to see in just what way all these diverse substances act. One is inclined to compare the production of light by chloroform or saponin to a process of cytolysis or to a stimulus reaction like artificial parthenogenesis. The photophelein of Cypridina or other extracts would then be comparable to the cytolytic substance in the blood of worms which causes development of sea-urchin eggs (11). The chloro form or saponin might be supposed to cause the solution of granules or globules (as can be observed in many cells) and the production of light to be connected with this solution process. But I have already given evidence (p. 178) to show that there are no granules unless ultra microscopic ones in the light-secretion of Cypridina, so that we must look to another interpretation.
Of many animal extracts tried on both concentrated and dilute photophelein, none will give light. Neither have I been able to obtain
light with any chemicals or the oxidizing substances—neutral ox blood alone or with neutral added, neutral potato juice alone or with neutral or As already pointed out (p. 177), this result is the direct opposite of the case in Pholas dactyl= as described by Dubois.
There is, then, in the non-luminous parts of Cypridina hilgendorfii a large amount of photophelein, but only a small amount even in a closely related non-luminous form. There appear to be only small amounts in other luminous forms not closely related to Cypridina. For instance, Cypridina photogenin will give a faint light with firefly photophelein, but it is not nearly so bright as with Cypridina photophelein nor as bright as that given by non-luminous Lewis extract. Unfortunately, no closely related luminous crustacean was available, so that the degree of speci ficity of photogenin and photophelein could not be determined. At least we may say that Cypridina photogenin and photophelein are specific to a certain extent, but not in the strict sense of the word.
The following tabulation gives the luminous animals which have been tried with Cypridina in concentrated solution and the character of the light resulting. None gives light in more dilute solution.
Owing to lack of material, the luminous fish Monocenfris japonica could be tested only in more dilute solutions, and with negative results, viz: