840 NATURE MAY 15, 1937 Molecules in Interstellar Space? A Possible Function of the Osphradium in the Gastropoda IN a recent note in NATURE\ and more in detail elsewhere•, Dr. T. Dunham, jun., has described his DESPITE the universal occurrence of the osphradium discovery of more interstellar lines due to K in the mantle cavity of marine Gastropoda and the (A 7699·03), Ca (A 4227), Ti + (A 3242·6 and others) large size to which it may attain, the current views and a number of other lines the origin of which has as to its function are unsatisfactory. It has been not yet been traced (A3957·7, A4300·3, A4232·6). considered (a) an organ for testing the water which We have to add to these Merrill's interstellar lines3 enters the mantle cavity (Bernardi), and (b) as a (A 5780, A 6284). chemo-receptor concerned with the detection of food Dunham's work and his discussion of the occurrence in water (Henschel", Brock3 ). of Ti +-lines forms a landmark in the story of inter· But the sea is a very constant medium, apart from stellar investigations, as it throws clear light on the regions near the shore or the mouths of rivers, and mechanism of excitation, and removes a good deal the osphradium is present in Gastropoda which live of misconception arising out of the former idea that in the open sea under conditions where the water only Ca+-lines, and the sodium D-lines occur in is never contaminated or diluted. There is cer­ interstellar space. tainly no correlation between the presence, or size, Dunham's discovery that only such Ti +-lines which of the osphradium and the possible need for arise from absorption in the lowest orbit of Ti + 'water testing'. The second theory can at best 2 4 have only a limited application, namely to pre­ (3d • 4s. F 312) occur as lines and th.at no Ti + atom in the next exCited state T1 + dacious carnivores or carrion feeders such as Nassa and Buccinum (studied by Henschel' and Brock3 (3d•. 4s. 4F , excitation potential 0·012. volt) occur 512 respectively). It cannot apply to browsing herbivores, in interstellar space, shows that the reactiOn between 4 matter and radiation in interstellar space is of a kind for example, Pterocera (Yonge ) or Littorina, deposit feeders such as Aporrhais which seek for food with which cannot be described in terms of any interspace 5 temperature. The temperature in interspace is very the proboscis (Yonge ), or plankton feeders such as 4 6 nearly absolute zero, and ionization is produced only Vermetus (Yonge ) or Crepidula (Orton ). Yet in all by the photochemical action of quanta meeting these, with the exception of Crepidula where it is atoms or ions after long intervals of time in space. reduced, the osphradium is well developed. More­ The recombination between ions and electrons also over, there is nothing in the evidence produced by take place at very long intervals. The result is that Henschel or by Brock inconsistent with the pos­ only such states of atoms and ions occur in inter­ sibility that the siphon is the chemo-receptor in stellar space as have infinitely long life. carnivorous species. This possibility is being in­ vestigated by us. The argument raises the question : Why should An alternative theory as to the function of the not molecules also occur in interstellar space ? In osphradium has been developed by us as the out­ fact, the above arguments, if forced to their logical come of work on the ciliary currents in the mantle conclusion, lead us to the view that we should have cavity of Aporrhais (Yonge5 ), followed by com· molecules in interstellar space. Merrill in fact notes parative work on a variety of common marine that the lines 1.. 5780·4, and A 6284·0 discovered by Prosobranchs and Opisthobranchs. It is suggested him are diffuse, and in course of a conversation told that the osphradium is concerned with the estimation me that they might be molecular in origin. In fact, of the amount of sediment carried into the mantle the line A 6283 ·0 appears decidedly to be due cavity by the water currents created by the lateral to molecular sodium, Na2, due to the transition cilia on the gills. Our reasons may be summarized as (Na3 : n"=O, n'=8). follows: This band is obtained in absorption in molecular ( l) Material carried into the mantle cavity is sodium, and according to the Franck-Condon prin­ divided into three portions. The heaviest material ciple, the transition is stro?-g as r" (internuclear is removed by way of the inhalent aperture by cilia 8 distance at the lowest state) 1s 3·07 x l()- em., and lining the mantle in this region. The finest material r' (internuclear distance at the excited state) is 8 is carried between and over the gill filaments and 3·66 x I0- em., so the transition n" = 0 ton' = 8 entangled in the mucus from the hypobranchial gland is the most probable. According to the arguments before being expelled via the exhalent aperture. presented here, no other line (or band) of Na, is Medium-sized particles are accumulated invariably likely to occur among the interstellar lines. along the line of the osphradium, before being carried Merrill's other line (1.. 5780) may be provisionally across the floor of the mantle cavity to the exhalent identified with a line of NaK (n" = 0, n' = 5), aperture. though in this case the identification is less sure. (2) The osphradium, besides possessing sense cells The molecule which is likely to be most abundant (well described by Bernardi and by Stork'), also in interstellar space is H 2 , but as it gives absorption possesses very many mucous glands. The secretion of lines only in the Lyman region, there is no possibility these masses gathers together the material which of our being able to prove its existence, but lines accumulates on the osphradium. Previous workers due to hydrides may be found amongst interstellar have made no suggestion as to the function of these lines. glands. 1\I. N. SAHA. (3) There is a general correlation between the Department of Physics, development of the osphradium and the degree of sediment to which the animal is exposed. For University, Allahabad. example, it is broad in mud- and sand-dwelling April 6. Prosobranchs, such as Ruccinum, Nassa, Pterocera, 1 NATURE, 139, 247 (1937). etc. ; linear in passive burrowers such as Aporrhais ' Pub. Ast. Soc. Pac., 49, 26 (1937). and plankton feeders such as V ermetus ; reduced in ' Pub. Ast. Soc. Pac., 43, 179 (1936). Crepidula, which is a plankton feeder normally raised © 1937 Nature Publishing Group.