March 3. 1910] 



NATURE 



have been unfortunate in timing it, and have missed the 

 continuous spells of strong sunshine 



We could not hope to attack the problem so successfully 

 here as in India, and it would be interesting to have' some 

 Indian work on the subject. The experiments of Mr. and 

 Mrs. Howard in conjunction with Mr. Leake on the 

 ■" fertilising influence of sunlight " may be expected to 

 throw a great deal of light on a verj- important problem. 



E. J. Russell. 



Rothamsted Experiment Station, Harpenden. 



The Spectrum of Bacterial Luminosity. 



I\ the course of some experiments on the phosphor- 

 escence of minerals, especially with regard to the emission 

 of ultra-violet radiation, it was suggested to me by Prof. 

 Strutt that it would be of interest to examine the spectrum 

 of the light from luminous bacteria. Through the kind- 

 ness of Sir James Deyvar, Prof. Strutt was enabled to 

 furnish me with a dish containing bacteria produced from 

 fish which, when viewed in a darkened room, were seen 

 to glow with a greenish-blue light bright enough to enable 

 one to read a watch. The dish was placed in front of the 

 slit of a quartz spectrograph of rather crude design, con- 

 structed with lenses of short focal length so as to utilise 

 the light available to the fullest extent. .A special rapid 

 photographic plate was first exposed to the radiation from 

 the bacteria for forty-six hours, and then to the light from 

 a cadmium spark for one second. 



The plate when developed exhibited strong evidence that 

 the spectrum of the light emitted by the bacteria consisted 

 of a continuous spectrum extending from wave-length 

 5000 (the lower limit of the sensitiveness of the plate) to 

 wave-length 3500 tenth-metres, together with a well- 

 marked bright band of wave-length 4000 approximately. 

 Practically the same result has been obtained from bacteria 

 produced from meat. The greater portion of the radiation 

 is absorbed by a film of nitroso-dimethylaniline. 



Mr. J. E. Barnard, in his article on luminous bacteria 

 (Nj\ture, April 10, 1902), states that the light emitted by 

 these organisms is confined to a small portion of the visible 

 spectrum, and never extends into the ultra-violet or infra- 

 red. The photographs I have obtained indicate that in 

 some cases these bacteria emit ultra-violet radiation, and 

 I hope with another spectroscope, now in course of con- 

 struction, to obtain more definite information. 



R. W. FORSVTJt. 



Royal College of Science, South Kensington, S.W., 

 March i. 



Self-fertilisation and Loss of Vigour. 



Some of your readers will remember that in the introduc- 

 tion to '* Cross and Self-fertilisation of Plants," Darwin 

 inserts a report by Sir Francis Galton on seven tables of 

 measurements relating to the relative heights of the offspring 

 of cross and self-fertilised plants. " It is a very remark- 

 able coincidence," says Galton, " that in the seven kinds 

 of plants the ratio between the heights of the crossed and 

 the self-fertilised ranges in five cases within very narrow 

 limits. In lea mays it is 100 to 84, and in the others it 

 ranges between 100 to 76 and 100 to 86." 



If Table .\ of Darwin's book be referred to, it will be 

 found that these ratios recur in many more than five cases. 

 I write to suggest — with great diffidence, as I am a mere 

 amateur in such matters — that the persistence of these ratios 

 is capable of simple explanation on the basis of the Men- 

 delian theory of heredity. 



The distribution or " array " of a Mendelian family, 

 crossed at random, is given by the expansion of (3D-I-R)". 

 where n = the number of pairs of characters involved, and 

 the powers of D and R respectively represent the number 

 of dominant and recessive somatic characters of each indi- 

 vidual. If, now, each individual be self-fertilised, the array 

 can be shown by simple algebra to become (jD-f-sR)"- 

 Similarly, in the next self-fertilised generation, the array 

 becomes (9D + 7R)", and so on. The average number of 

 dominant characters in each generation is, consequently, 

 5« ; %n ; y^n, &c., which give the ratios 100 : 83 : 75, &c. 



It is surely som.ething more than a " remarkable coinci- 

 dence " that these ratios agree in so many cases with the 

 ratios observed by Darwin? A. B. Bruce. 



School of .Agriculture, Cambridge, February 19. 



NO. 2105, VOL. 83] 



Vision and Colour Vision. 



With reference to the comment on my lecture at the 

 Royal Societ>' of Arts in Nature of February 17, I did 

 not give the evidence in favour of the visual purple being 

 the visual stimulus transformer on account of the time 

 at my disposal. This evidence is very strong, and the 

 facts are inexplicable on any other hypothesis. Many 

 physiologists have tried to assign different functions to 

 the rods and cones, but these theories have failed because 

 all the functions which were said to be the exclusive 

 property of the rods have been found, only gradually 

 diminished, in the fovea, in which only cones are present. 

 For instance, von Tschermak, Hering, Hess, Garten, and 

 others, have found the Purkinje phenomenon, the varia- 

 tion in optical white equations by a state of light and 

 dark adaptation, the coloOrless interval for spectral lights 

 of increasing intensity, the varying phases of the after- 

 image, in the fovea, only gradually diminished. The 

 complete absence of any qualitative change between the 

 foveal and extra-foveal regions is a very important fact 

 in support of the hypothesis that the visual purple is the 

 visual substance. There is also the fact, mentioned by 

 Helmholtz, that a perceptible interval elapses before we 

 see with the fovea, after the rest of the retina, when the 

 eye has been previously some time in darkness. Hess has 

 also pointed out that the recurrent image is present, but 

 retarded at the yellow spot. All these observations and 

 many others agree with my statement that the visual 

 purple can be seen between but not in the cones of the 

 fovea. F. W. Edridge-Grees. 



Hendon, Februar\- 19. 



The Methods of Bird Fanciers. 



May I ask for information on the following matter? 



Happening to be walking in a poor quarter of Acton 

 (Chiswick) with a friend, we were astonished to see hang- 

 ing outside a house, on either side of the door, two small 

 bird-cages completely enveloped with dark cloths carefully 

 fastened. The cages evidently contained birds, for from 

 one of them came the song of a chaffinch. 



Had the birds suffered the torture of having their eyes 

 put out to make them sing, or is this a method resorted to 

 instead of blinding them? 



The caging of wild birds is so ver\' cruel that it should 

 be exposed in all its barbarous ways. 



Some of the wild birds are kept in such small cages 

 that there is scarcelv room for them to turn round. 



E. L. 



It is customarv- for bird fanciers amongst the lower 

 classes to match one chaffinch against another, often in 

 public-houses, the bird which sings the largest number of 

 notes being adjudged the victor. When the cages are 

 carried about they are usually wrapped up in dark cloths, 

 and it is said that one of the objects of keeping the birds 

 in the dark is that they should imagine it is night while 

 they are covered, and that on the cloth being removed, 

 thinking it is day, they burst forth into song. As it 

 is believed by some that birds sing l)etter when they are 

 blinded, it may be, as " E. L." suggests, that the covers 

 were used in the case mentioned either to avoid practising 

 the cruelty of putting out the birds' eyes or so that the 

 fancier might not render himself liable to the punishment 

 for doing so. More likely the birds that were kept covered 

 were newlv caught, and the object was to prevent them 

 from dashing themselves against the bars of the cages in 

 their endeavours to escape. As has often been pointed 

 out, one reason for the smallness of the cages used is to 

 lessen the danger of the birds killing themselves, as in a 

 larger space they could begin to fly and would strike with 

 greater force. Wilfred Mark Webb. 



Title of the Natural History Museum. 



In Nature of February 24 (p. 489) Mr. Hobson suggests 

 as both " suitable and adequate " that it should be called 

 the " British Museum of Natural History." 



Whv not omit " British " and " of," re-arrange the order 

 of the' words, and call it " The Natural Histor>- Museum," 

 adding " London " if necessary? 



Torquay. F- How.ard Collins. 



