July 3, 1914] 



SCIENCE 



33 



Making preparations of tissues is greatly 

 facilitated by the use of this medium, and the 

 comparatively constant composition of the 

 mixture renders the results obtained through 

 its use more uniform than those secured by 

 the employment of lymph or plasma. The im- 

 planted cells get what very nearly corresponds 

 to their natural food in the serum of the 

 blood, and the gelatine, while apparently acting 

 in no way injuriously to the cells, affords a 

 means of appealing to their thigmotactic pro- 

 clivities that is ordinarily supplied by the 

 fibrin of clotted plasma. 



The outgrowth of epithelium in this miedium 

 is remarkable. In some eases it has been over 

 twenty times the superficial area of the im- 

 planted tissue. As a rule the tissues thrive 

 better than in plasma or lymph. It is com- 

 paratively easy to subculture the tissues, since 

 the gelatine dissolves in Ringer's solution, and 

 by washing the preparations in this fluid they 

 may be readily freed, and then transferred to 

 a fresh culture medium. I have transferred 

 pieces of epithelial tissue several times in suc- 

 cession, and kept them thriving for three 

 months. Cell divisions have been repeatedly 

 seen in epithelial cells in this medium. In a 

 piece of tissue put up on February 17 and 

 changed to fresh culture fluid three times 

 afterwards, I observed several mitotic figures 

 in epithelial cells on April 8, fifty days after 

 the preparation was made. The chromosomes 

 could be seen with great distinctness in the 

 living material. In one cell first seen in the 

 prophases of division, the chromosomes were 

 seen to align themselves in the equatorial 

 plate, then to be dravm apart, and finally to 

 become constituted into the two daughter 

 nuclei; at the same time the constriction in 

 two of the cell body could be distinctly fol- 

 lowed. Over a dozen other mitotic figures in 

 various stages were observed in the same piece. 

 The preparation had been washed in Ringer's 

 solution and transferred to new culture medium 

 a few days previously, after which it had 

 taken on a new lease of life. The division 

 figures were all seen in a transparent sheet of 

 epithelium that had spread out in contact with 



the cover slip supporting the hanging drop 

 culture. S. J. Holmes 



Univbrsitt op California, 

 Berkeley, Calif. 



ON THE CHEMICAL NATUEE OP THE LUMINOUS 

 MATERIAL OF THE FIEEFLY 



Our knowledge of the chemistry of light 

 production by organisms may be summed up 

 in the statement that phosphorescence is due 

 to the oxidation of some substance formed in 

 the cells of the animal. As with other oxida- 

 tions, both water and oxygen must be present. 

 If either water or oxygen are absent the photo- 

 genic substance will not be used up by oxida- 

 tion. Luminous tissues if dried rapidly may 

 be ground up and preserved indefinitely, and 

 at any later time, if moistened in the presence 

 of oxygen, will phosphoresce. This old and 

 important discovery makes the investigation 

 of the chemical nature of the luminous sub- 

 stance relatively easy. The dried powder of 

 the luminous organ may be extracted with : (1) 

 Oxygen-free watery solvents, or (2) water-free 

 solvents (as ether, chloroform, etc.) with or 

 without oxygen. 



The earlier workers supposed the photogenic 

 material to be phosphorus or phosphine. 

 These views require no comment to-day. 

 Later suggestions have been that the substance 

 is a fat, an albumin, a lipoid (lecithin), a 

 nucleoalbumin or a lecithoprotein (phos- 

 phatid). It is obviously desirable to know 

 whether the substance is fat-like or protein in 

 nature. The fact that phosphorescence ceases 

 as soon as the moist luminous material is 

 heated to 100° proves nothing, for, like organic 

 oxidation in general, an oxidizing ferment is 

 probably involved, and it is this oxidase which 

 may be destroyed on heating. 



I can state definitely that the " luciferin " 

 of the common fire-fly is not a true fat or any 

 fat-like body such as lecithin. The dried 

 material may be extracted with anhydrous 

 ether and the ether extract evaporated to 

 dryness. On adding water or a watery extract 

 of luminous organ (to add an oxidizing 

 enzyme) or potato juice (to add an oxidase) to 

 the residue no phosphorescence took place; on 

 adding water to the original ether extracted 



