DESICCATION AND EXTRACTION WITH FAT SOLVENTS.
The experiments recorded herein have been made during a period of two years on several different species of firefly—the American Photuris pennsylvanica and Photinus pyralis, the Japanese Luciola vitticollis and L. parva, and the West Indian "cucullo," Pyrophorus noctilucus and P. havaniensis. All the species are essentially similar in behavior, and in general the statements apply to all.
Contrary to the condition in Cypridina, the photogenic substance is burnt within the cell which forms it and is found there in the form of granules scattered through the cytoplasm. The histological struc ture of the luminous tissue has been well described by many observers [Townsend (is), Lund (3), Dahlgren (Is), Vogel (43), Bongardt (44), Geipel (43), Williams (46)] and need not be considered here.
The old observation that firefly luminous tissue can be dried and ground up and will phosphoresce when water containing oxygen is again added, gives a simple chemical method of investigating the nature of the photogenic material. The dried material may be extracted with water-free solvents (since the photogen does not oxidize in absence of water) and extracted material as well as the residue from evaporation of the filtrate may be tested for phosphorescence by adding water. The results indicate that a large number of fat solvents will extract nothing from the dried tissue and leave the photogenic material un harmed. Indeed, the material may be extracted with boiling ether for 24 hours without impairing its power to phosphoresce. Boiling alcohol does destroy the power to phosphoresce, and the nature of its action is discussed below. These results, as well as the previous experi ments of McDermott (20 and 21) and Dubois (22), using fresh watery material, show conclusively that the photogenic substance is not a fat or fat-like body of any kind. The results are given in table 9, which also gives the time of extraction and the temperature.
A plus sign indicates phosphorescence when water is added and a minus sign indicates no phosphorescence. Both the original extracted material and the residue of the filtered extract evaporated to dryness were examined. The results indicate not only that the photogenic substance is not a fat, but also not a lecithin. I am aware that the lecithins are difficult to extract in Coto from the cell, but this can be accomplished by a mixture of hot ether and alcohol, and yet a mixture of hot ether and alcohol will extract nothing which will phosphoresce from the firefly powder. We may safely say that the photogen is not a lecithin.
Of all the solvents tried, only hot alcohol and cold amyl alcohol and ethyl butyrate gave results that would indicate a possible solution of the photogenic substance; and yet there is nothing in the evaporated filtrate that will phosphoresce when water or a neutralized 3 per cent solution of is added. Thinking that a second substance might be necessary and that this had not been extracted by the fat solvents, although the photogen had, the filtrate was also tested by adding a water extract of firefly organs, fresh or preserved with toluol or chloro form, and also by potato-juice which contains considerable quantities of oxidizing enzymes. In no case was phosphorescence observed. The boiling ethyl alcohol,' cold amyl alcohol, and ethyl butyrate must, therefore, break up the photogen. It is the alcohol itself and not the temperature (78.4°) of boiling alcohol which is responsible for the destruction of the photogen, as the dried powder will withstand this temperature for 24 hours without any appreciable diminution in its power to phosphoresce. McDermott finds that liquid sulphur dioxide and liquid ammonia also destroy the photogenic power (2o).