Aur.usT I, 1907] 



NA rURE 



543 



type of seed habit than has hitherto been met with in 

 Cryptogams. The niegasporange gives rise to but one 

 thin-walled spore, which in development and structure 

 resembles an embryo sac and germinates in silii. An 

 integument surrounds the sporange, leaving but a small 

 orifice as micropyle. This is surrounded by numerous long 

 processes of the integument, which formed a collecting and 

 incubating apparatus for the microspores. There is no 

 trace of an envelope about the microsporange. The 

 carpellary leaf was shed at maturity, and resembles a 

 winged seed. 



Disregarding the structural modifications of the mega- 

 sporophyll, the nearest affinity of Miadesmia among forms 

 so far known seems to be with the non-specialised species 

 of Selaginella, such as SelagiiicUa selaginoides, but the 

 foliage leaves show the archaic leaf-base comparable with 

 that of Lepidodendrese. 



" The Inhibitory Action upon Subsequent Phago- 

 cytosis, exerted on Active Normal Serum by Inactive 

 Normal Serum through which Bacilli have been passed." 

 By I. C. G. Ledingham. Communicated bv Dr. C. J. 

 Martin, F.R.S. 



When inactivated normal serum is digested with tubercle 

 bacilli, and finally freed therefrom by the centrifuge, it 

 is found that the supernatant fluid has the property of 

 inhibiting to a great extent the opsonic action of fresh 

 normal serum, not only Inwards the tubercle bacillus, but 

 also towards the Staphylococcus pyogenes aureus. The 

 author interprets the phenomenon thus : — The amboceptors 

 of heated normal serum combine with the tubercle bacilli 

 and also with their free receptors, which remain in the 

 supernatant fluid after removal of. the bacilli. When this 

 supernatant fluid containing the " free receptor 

 amboceptor" combination, is added to fresh normal serum, 

 the latter's complement becomes fixed, and consequenth 

 in the presence of fresh bacilli, opsonic action is inhibited. 

 The experimental results obtained lend support to the view 

 that the opsonic action of normal serum depends on the 

 cooperation of complement with normal amboceptor. 



June 20. — " Preliminary Note on a New Method o( 

 Measuring directly the Double Refraction in Strained 

 Glass." 'By Dr. L. N. G. Filon. 



If a plane wave of light be passed horizontally through 

 a rectangular slab of glass under flexure in a vertical plane, 

 it is broken up into two components polarised horizontally 

 and vertically. 



The light of either component suffers, owing to the 

 stress, an additional retardation proportional to its distance 

 from the " neutral axis," i.e. the mid-level of the slab. 

 Thus the wave-front on emergence is no longer vertical, 

 but has suffered a deviation proportional to the bending 

 moment applied. The two components, however, are 

 deviated by different amounts. 



If the light be then analysed by a grating, the lines of 

 the spectrum formed will bo shifted, in consequence of the 

 change in the angle of incidence. In addition, owing to 

 the different shifts of the two components, each line appears 

 doubled. 



Experiment shows that the effect is quite measurable, 

 and provides a new method for measuring directly the 

 doubly refracting effect of stress, giving, not only the 

 1 ifference between the retardations of the two components, 

 '..»ut the absolute amounts of each. 



With a grating of 14,000 lines to the inch, the maximum 

 separation of the components, for lines in the vellow. was 

 about the distance between the two D-lines. 



" On the Origin of the Gases evolved bv !\Iinoral 

 Springs." By the Hon. R. J. Strutt, F.R.S. 



It has long been known that thermal springs, such as 

 those at Bath, give off considerable quantities of gas, 

 which bubbles up with the water, and consists, for the 

 most part, of nitrogen. Of recent years, interest in this 

 subject has been revived by Lord Rayleigh's observation 

 that helium and argon arc present along with nitrogen. 



It has been found that such gases, when fresh, are rich 

 in radium emanation, and that the deposit thrown dow-n 

 by the water on standing cont.ains a notable quantity 01 

 radium. It is natural to connect this observation with the 



discharge of helium by the springs. The author was 

 formerly inclined to think that the facts were most easily 

 explained by supposing that the supplies of helium and 

 radium were derived from the disintegration of uranium 

 lodes at a great depth by the water, but this view scarcely 

 seems compatible with the universal presence of helium 

 and radium in mineral springs, which has since been 

 brought to light ; for uranium lodes are very rare near the 

 earth's surface, and there are fatal objections to supposing 

 that metal to be generally more abundant at greater 

 depths. 



The unexpectedly large quantities of radium found in 

 common rocks led the author to suspect that perhaps they 

 might after all be able to supply the helium and radium 

 products, as well as the ordinary gases and saline con- 

 stituents of the spring. With the view of deciding this 

 question, he has examined the inert portion of the gases 

 given off by several varieties of rock on heating. The 

 subject has attracted some attention from previous experi- 

 menters. 



The results for two normal rocks were as follows : — 



Matopo Granite. Quantity taken, 850 grams. 

 The inert residue consisted of 



Nitrof;en ... ... ... ... ... 11 c.c. 



Argon 



Helium 



Neon 



Syenite Rock, ill. Sorrel, Leicestershire. 



taken, 900 grams. 

 Inert residue — 

 Nitrogen 



Argon 



Helium 

 Neon 



o'i4 c.c. 

 0'04 c.c. 

 I races 



Quantity 



9 c.c. 

 o 026 c.c. 

 o 010 c.c. 

 traces 



In both these cases, the vacuum tube, after removal of 

 argon, gave a brilliant yellow helium glow. 



We may compare these analyses with the composition of 

 the Bath gas, as a type of the gases evolved by mineral 

 springs. The total volume of inert gas (mainly nitrogen) 

 is taken as 100. 



These figures make it fairly clear that there is a general 

 resemblance between the gases of mineral springs and the 

 gases of rocks, so far as nitrogen and the other inert con- 

 stituents are concerned. 



In addition to these constituents, rocks give off hydrogen, 

 carbonic oxide, carbonic acid, and a little methane. The 

 two former are probably secondary products, produced by 

 chemical actions set up on heating. Carbonic acid is re- 

 presented at the spring by the dissolved carbonates of the 

 mineral w'ater, while methane is present in the evolved 

 gases. The author tliinks, therefore, that we may con- 

 sider that the disintegration and partial solution of ordinary 

 rocks by water at a high temperature accounts for the 

 gaseous, as well as the solid, products, delivered by springs 

 such as those at Bath. 



With regard to the primary origin of the argon and 

 peon contained in rocks, the author has no theory to offer. 

 It is natural, however, to associate the helium of rocks 

 with the radium they contain. The relative quantities are 

 ouite in accordance with such a view, for the ratio is of 

 the same order as in the strongly radio-active minerals. 

 The author hopes to discuss this subject in detail in a 

 future paoer. He has found at least traces of helium in 

 almost all of a considerable collection of ores and other 

 minerals, but hitherto only one case has been found — in 

 certain beryls — where there seems to be sufficient reason 

 to look for any other cause than traces of the radio-active 

 elements to explain its presence. The evidence so far 

 obtained is not favourable to the view that the ionising 

 radiation from ordinary substances is accompanied bv 

 production of helium. 



NO. 1970, VOL. 76] 



