578 



NATURE 



[May 6, 1922 



Letters to the Editor. 



\The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return^ or to correspond with 

 the writers of., rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.'] 



The Buoyancy of the Son-fish. 



About the end of August numbers of sun-fish 

 {Orthagoriscus mola) make their appearance off the 

 north coast of Ireland floating passively on the surface 

 of the sea. The positive buoyancy, while not so 

 great as to prevent the fish from submerging when 

 attacked, constitutes a constant upward drag which 

 brings it back to the surface as soon as it stops 

 swimming. So far as we know, the bodies of all 

 other fish have a specific gravity greater than that 

 of sea-water, and the swim-bladder, where it exists, 

 contains the necessary amount of gas to compensate 

 for this and bring the body of the fish to neutral 

 buoyancy. 



The sun-fish has no swim-bladder, and on cutting 

 up a fish and throwing pieces of the various organs 

 overboard, it was found that everything sank except 

 the liver and the skin. The Hver floats no doubt 

 because of the large quantity of fat it contains. 

 The skin is 2 -2 J inches thick and, the fish being flat, 

 forms a large proportion of the body : it is evident 

 that the fish floats passively on account of this 

 buoyant jacket. 



The skin is made of a tough elastic material, 

 slimy to the touch, resembling rather soft cartilage : 

 as a whole it is stiff enough to form what may be 

 described as a rigid coat. For more detailed ex- 

 amination a number of slices were preserved in sea- 

 water formalin : the slices had not changed in their 

 appearance or proportions, and this pickled material 

 probably represents fairly the fresh condition apart 

 from such features as the solubility of the mucus, 

 etc. The epidermis is 1-2 mm. thick ; internally 

 the skin is bounded by the very thin parietal peri- 

 toneum : the rest is uniform in appearance and 

 shows microscopically a felted mass of thin wavy 

 fibres arising stellately from connective tissue cells. 

 There are a few rather thicker straight fibres but 

 nothing of the nature of trabeculag or struts. A few 

 canals — presumably mucous ducts — are found here 

 and there. No stainable fat is present, nor can any 

 be obtained from dried material by extraction with 

 ether, chloroform, or petrol. 



After washing out the salt in distilled water, the 

 specific gravity of the substance of the skin was 

 found to be 1013 to 1016 with a mean of 1014 by 

 weighing in air and water and floating bits in salt 

 solutions of different strengths. It is difficult to 

 get very precise results since one has to start with 

 pieces in the rather indefinite state of being " surface 

 dry." The specific gravity of pieces soaked in o-g 

 per cent. NaCl solution was 1021. This may be 

 taken to be somewhat near the natural gravity since 

 it is known that the concentration of the body 

 fluids of teleostean fish corresponds with that of 

 mammals and is much less than sea-water. Taking 

 the gravity of sea- water as 1026, these figures are 

 compatible with the observation that the whole 

 fish is just buoyant. 



The most remarkable thing is that the percentage 

 of solids in the skin washed out in distilled water is only 

 about 3-7 per cent., figures varying from 3 -5 to 4-2 

 being given by different pieces while the loss of weight 

 on drying in vacuo over sulphuric acid is practically 



NO. 2740, VOL. 109] 



the same as the loss in an oven at 95° C. Histo- 

 logically the larger part of the skin substance appears 

 to be made of connective tissue fibres, and it is 

 extraordinary that 2 per cent, or less of the mucoid 

 material can give, when it is swollen with water, 

 a tissue the mechanical firmness and rigidity of the 

 skin. 



The specific gravity of the dried solids, by floating 

 in chloroform-petrol mixtures, was 1-335. Calcula- 

 tion from this gives a specific gravity of 10 10 or there- 

 abouts for the undried material. The difference between 

 this and the determined value of 1014 (involving a 

 value of about i'6 for the solids) may be an error 

 of observation or indicative of a condensation of 

 the mucoid material when it is swollen in water, 

 such as is known to occur with starch, gelatine, and 

 proteids (Chick and Martin, Biochemical Journal, 

 vii. (1913). 92). 



After formalin fixation, the mucus is not soluble 

 in dilute sodium carbonate, and once the skin has 

 been dried in vacuo it will _not swell up again in 

 water, dilute acid or alkali. 



G. C. C. Damant. 

 A. E. Boycott. 



Thursford, East Cowes. 



Haloes and Earth History. 



In continuation of my letter on this subject in 

 Nature of April 22, p. 517, fifty additional measure- 

 ments of the small Ytterby haloes have been made. 

 The same consistency among the readings is notice- 

 able. The mean result is a radius of -0-0052 mm. 

 Introducing two corrections not previously applied 

 (for the somewhat higher stopping power of this 

 mica and for the fact that in such measurements 

 we do not generally deal with the extreme range) 

 I find that the range in air might be as much as 1-4 

 or even 1-5 cm. The nuclear correction would reduce 

 this a very little. 



The consistency of measurements among these 

 haloes is, I think, even greater than would be found 

 to obtain among normal haloes. The law prevail- 

 ing among halo-dimensions is only apparent upon 

 comparison and classification. It is by no means 

 prima facie evident. It was just for this reason that 

 it for so long escaped notice. 



There is evidence that some of the larger sized 

 Ytterby haloes deserve consideration as constituting 

 a true radioactive development. Their radius is 

 consistently o-oo86 mm. The nucleus is far too 

 small to account for the difference. With all allow- 

 ances (save that for the nucleus) this comes out as 

 2-4 cms. in air at 15° C. This is suggestively hke 

 that of Ui (2-50). But we seem debarred from the 

 tempting conclusion that hibernium may be a proto- 

 uranium by the time-difficulties involved. 



The paragraph in my letter referring to the possi- 

 bihty that the Ytterby haloes might date back to 

 a prior geological era requires some explanatory 

 amendment. It would be better to speak of the 

 Archean as what (as I beUeve) it really is— the record 

 of a past geological era ; a material record finally 

 brought to an end by thermal changes sufficient to 

 evaporate the oceans. The reading of the halo — 

 could we read it aright — would then assign a date to 

 the formation of the containing mica. Upon the 

 prima facie evidence this date is very remote. That 

 is all I have to say upon this point. 



There are, as I have intimated, possible alternatives 

 to the view that very great time intervals are involved. 

 The element responsible may emit a-rays the con- 

 nection of the range of which with the radioactive 



