286 



NATURE 



[July 19, 1888 



From this investigation, the isolation of uric acid proves the 

 renal function of the five pouches of the stomach of the Asteridea. 

 These pouches are the homologues of the organs of Bojanus 

 and nephridia in the Mollusca, the green glands of the Crustacea, 

 and the segmental organs of worms. 



II. The Salivary Glands of Sepia officinalis and Patella 

 vulgata. 

 The author has already made a complete study of the 

 nephridia and the so-called "livers" in both these forms of 

 the Invertebrata (see the memoirs, loc. cit.). Since then he has 

 studied the chemico-physiological reactions of the secretion 

 produced by the salivary glands of the cuttle-fish and the 

 limpet ; these organisms representing two important orders of 

 the Mollusca. 



1. Sepia officinalis. 



There are two pairs of salivary glands in Sepia officinalis. 

 The posterior pair, which are the largest, lie on either side of 

 the CESophagus. The secretion of the posterior glands is poured 

 into the oesophagus, while the secretion of the smaller anterior 

 pair of glands passes directly into the buccal cavity. . This 

 secretion was tested by similar reactions to those described in a 

 former paper (Edinburgh Roy. S.oc. Proc, vol. xiv. p. 230) and 

 with similar results. ... 



There is .much in favour of the supposition that the diastatic 

 ferment found in these secretions is produced as the result of the 

 action of nerve-fibres (frpm the inferior buccal ganglion) upon 

 the protoplasm of the epithelium cells of the glands. 



The author intends to examine various organs in other genera 

 and species of the Decapoda ; especially those inhabiting the 

 Japanese seas. 



2. Patella vulgata. 



The two salivary glands of Patella are well-marked and 

 situated anteriorly to the pharynx, lying beneath the pericardium 

 on one side, and the renal and anal papillae on the other. They 

 are of a yellowish-brown colour and give off four ducts. The 

 secretion of these glands was examined by the same method 

 applied to the salivary glands of Sepia officinalis, and with 

 similar results. 



The following table represents the constituents found in the 

 salivary secretions of the two orders of the Mollusca aleady 

 investigated : — 



From these investigations, the salivary glands of the Cephalo- 

 poda and Gasteropoda are similar in physiological function to 

 the salivary glands of the Vertebrata. 



III. The "Liver" of Carcinus mcenas. 



The " liver " of Carcinus mcenas consists of two large glands 

 on each side of the stomach, and extending the whole length of 

 the cephalo-thorax. These organs are of a yellow colour, and 

 consist of numerous csecal tubes arranged in tufts which are 

 easily seen in a dissection beneath the surface of water. 



The secretion of the so-called "liver" of Carcinus mcenas, 

 when freshly killed, gives an acid reaction. 



From the reactions detailed in the paper the conclusion to be 

 drawn is that the so-called "liver" of Carcinus maznas is pan- 

 creatic in function, i.e. its secretion is more like the secretions 

 of the pancreas of the Vertebrata than those of a true liver. 



Some biologists look upon the vertebrate liver, pancreas, and 

 salivary glands as differentiated bodies of an original pancreas 

 of the Invertebrata. But have not very many forms of the 

 lower animals similar salivary glands to those found in the 

 Vertebrata? And is not the so-called "liver" of the Inverte- 

 brata a true pancreas capable of producing the same chemical 

 and physiological reactions as the pancreas of higher forms ? 

 1 Edinburgh Proc. Roy. Soc, vol. xiv. p. 236. 



Physical Society, June 23. — Prof. Reinold, F.R. S., Presi- 

 dent, in the chair. — The following communications were read : — 

 The photometry of colour, by Captain Abney, F.R. S. This 

 relates to the measurement of light reflected from coloured sur- 

 faces and pigments as compared with the quantity reflected 

 from white or black. The apparatus used in the investigation 

 consisted of a spectroscope and camera similar to those used by 

 the author for the production of a patch of monochromatic light, 

 and a small shadow photometer served for the measurement. 

 The screen was made of two parts — one the colour to be tested, 

 and the other white or black according to the standard being 

 used ; and the stick was arranged so that the shadows fell near 

 the junction of the two parts. Light reflected from the surface 

 of the first glass prism served to illuminate one shadow ; and for 

 the other, monochromatic light of any desired colour could be 

 used. The intensities were adjusted to equality by cutting off 

 more or less of the stronger light by means of a revolving wheel 

 with adjustable sectors, the opening of the sectors being a 

 measure of the luminosity of the pigment. In another arrange- 

 ment a double-image prism was used to separate the spectrum 

 into two parts. Monochromatic light from one part passed 

 direct to the screen through sectors in a rotating wheel, and 

 monochromatic light from the other spectrum was reflected on the 

 screen at a sufficient azimuth to give a separate shadow, by 

 means of two total reflection prisms. The losses by reflection 

 were allowed for by observing the position of the adjustable 

 sectors required to give equal intensities on a white screen. From 

 the results obtained "colour curves " can be plotted for different 

 pigments, &c, and templates constructed which, when rotated 

 in the path of a spectrum, reproduce the corresponding colour. 

 Carmine, sky-blue, and gold were thus reproduced. By means 

 of templates constructed from "colour curves" any colour may 

 be reproduced at any future time. In course of the experiments 

 many interesting observations on colour-blindness have been ob- 

 tained by the author and General Festing, some of which were 

 described. A question was asked as to whether it was possible 

 to reproduce any given colour, for no two arc lights could be ex- 

 pected to give exactly equal intensities in all parts of the spectrum. 

 Dr. Thompson requested information regarding the effect of 

 absorption by the different thicknesses of the prism through 

 which the light passed, and thought the results obtained might 

 be different if prisms of other materials were used. The fact 

 mentioned in the paper as to the sky being greenish is well 

 known to artists, who usually mix cobalt blue with yellow to 

 produce the required tint. Dr. Thompson also reminded the 

 members of an experiment he brought before the Society some 

 years ago, in which grass seen through a solution of perman- 

 ganate of potash appears bright crimson when compared with red 

 colours seen through the same solution. In reply. Captain Abney 

 said that colours could be imitated whatever the source used to 

 produce the spectrum, for the resulting colour is the same as that 

 seen when the "original " is viewed by light from that source. 

 Regarding absorption, &c, by the prism, he did not think any 

 appreciable difference was produced, for the results obtained 

 when using the recomposed spectrum as white light were the 

 same as those got by using light reflected from the surface of the 

 first prism. In conclusion, he directed the attention of physicists 

 to Lord Rayleigh's papers on sky colours, &c, published in the 

 Phil. Mag., which would well repay very careful study. — Note 

 on continuous current transformers, by Prof. S. P. Thompson. 

 Two classes of transformers are considered, viz. motor-generators 

 and commuting transformers, in which a two-circuit armature is 

 fixed in a revolving magnetic field. Such a field may be pro- 

 duced by using a fixed gramme ring as the field- magnet, and 

 rotating the brushes round its commutator. The formulae ob- 

 tained apply equally to both classes. If c x c 2 be the numbers of 

 primary and secondary wires on outside of armature ; Ej E 2 , 

 e \ e 2> h *2> r i r -2> tne E.M.F., potential difference at ter- 

 minals, currents, and resistances of primary and secondary re- 

 spectively, then it is shown that <? 2 = ke x - [r 3 + k"r^)i, where 



k — £?, which is called the "co-efficient of transformation." Thus 



the potential difference is the same as if the dynamo part had its 

 resistance increased by k 2 r v As the currents in the primary 

 and secondary are in opposite directions, the effective self- 

 induction will be very small, hence such machines can be run 

 with little or no sparking. In a previous paper by the same 

 author, similar properties as regards self-induction and resistance 

 were shown to exist in alternating current transformers. From 

 the above equation it is evident that a motor-generator cannot be 



