tions it was not possible to assign to it even an approximate limit. There was no increase of the absorption in the position of the urobilin band.

Treatment with zinc chloride and ammonia did not produce any fluorescence.

The alcoholic solutions always showed the same rich yellow or orange tint, and could be kept for a long time without undergoing any appreciable change; but aqueous solutions kept in stoppered bottles tended to assume a brown tint on standing, even when dilute, and this change was precipitated by evaporation or warmth. In this respect my product behaved just like urochrome.

The tendency of the aqueous solutions to undergo this change could be restrained by the addition of a little ammonia.

Alkalies did not appreciably alter the tint of dilute solutions, but more concentrated ones were slightly browner when alkaline than in the neutral condition.

Small additions of mineral acid produced no immediate change, but larger quantities quickly changed the colour to a reddish-brown. Solutions of the pigment were decolorised by nascent hydrogen produced by the action of hydrochloric acid upon zinc. This is only to be expected, seeing that it is a known fact that the urine is itself decolorised by similar treatment.* The destroyed colour was not restored by hydrogen peroxide.

Action of Mineral Acids upon the Pigment.

Solutions of the yellow pigment when warmed with nitric acid remained clear, but took a distinctly brighter yellow tint. On the addition of ammonia to alkalinity the yellow colour changed to a rich orange, the changes of tint being exactly similar to those which con. stitute the xanthoproteic reaction. This reaction seemed to be due to a change in the pigment as a whole, and not to any traces of impurity present.

Heated over the water bath with the addition of sulphuric or hydrochloric acid, the changes observed were uniform with all specimens of the indigo-free pigment which were subjected to this treatment, and were the same whichever of the two acids was employed.

The colour of the liquid quickly changed to reddish-brown, and on evaporation to dryness a nearly black residue was left. This residue, when treated with water, yields an orange-coloured solution, resembling the original liquid in colour, but darker in tint. This aqueous extract left on evaporation a brown residue, which was scarcely soluble in alcohol, but which communicated a yellow colour to chloroform. * Salkowski und Leube, Die Lehre vom Harn,' 1882, p. 14.

VOL. LV.

2 F

From the remainder of the original residue alcohol extracted more pigment, and hot alcohol more still, the liquid assuming a sepia tint, and showing no absorption bands. The hot alcoholic solution deposited, on cooling, a dark, pulverulent sediment, which, examined microscopically, was found to be amorphous. A black residue still remained which was insoluble in water, alcohol, and dilute acids, was scarcely soluble in amylic alcohol, but was readily dissolved by strong ammonia (the uromelanine of Thudichum). The alkaline solution gave no absorption bands.

After extraction with water the original residue communicated a yellow colour to ether, but no substance resembling the omicholic acid of Thudichum (which is readily soluble in ether with a fine red colour) was obtained.

Frecipitants of the Yellow Pigment.

In its behaviour towards metallic salts the pigment obtained by my process exhibited the closest resemblance to the urochrome of Thudichum.

The solutions were almost decolorised by the acetates of lead, by nitrate of silver, and by phosphotungstic and phosphomolybdic acids, which all threw down precipitates containing the bulk of the pigment.

Mercuric acetate decolorised the solutions completely, a yellow precipitate being formed, from which the colouring matter could be readily extracted with alcohol acidulated with hydrochloric acid, but apparently not without some change, evidenced by its reddish-brown colour.

Mercurous acetate had not the power of throwing down the pigment from its solutions.

Behaviour of the Pigment towards Uric Acid.

If to a solution of colourless urate, obtained from snake's excrement, some of the yellow pigment was added, and if the conditions of the experiment were so adjusted that crystals of uric acid are slowly deposited from the solution, these crystals resembled those which compose the yellow or brown variety of uric acid sand, and had, moreover, the ordinary urinary forms, the familiar whetstone shape preponderating. I have, indeed, specimens of crystals so obtained which are quite indistinguishable from those of the natural urinary sediments.

This experiment is difficult to carry out satisfactorily, chiefly owing to the instability of the isolated pigment. If the crystals are too quickly deposited they have the whetstone form, but are only

faintly tinted. If acid is added they have a brown colour like that of crystals thrown down on the addition of acid to urine.

The converse experiment to this was performed some years ago by Ord,* who showed that, on repeatedly redissolving and reprecipitating urinary uric acid, the crystals lost their colour, and, at the same time, tended to assume the tabular forms of those of pure uric acid.

The above result lends strong support to the view that the pigment is isolated by the alcohol process in the form in which it actually exists in the fresh urine, and confirms the statement that it plays an important part in determining the forms which the crystals assume.

Another fact which is demonstrated by this experiment is that the yellow pigment is one of those which colours the urinary crystals, although it does not stand alone in this respect. I do not, however, propose to enter further into this subject here, as I hope to deal with it at length in a separate paper, but I may mention that crystals of uric acid which are deposited from a solution of urobilin are colourless and exhibit no modification of form, resembling, in every respect, those thrown down from pure aqueous solutions of urates.

Summary and Conclusions.

There cannot, I think, be any doubt that the substance isolated from the normal urine by the process here described is that to which its colour is almost entirely, if not entirely, due, and, since solutions of this substance do not fluoresce with zinc chloride and ammonia, show no absorption bands, and cannot be got to show a urobilin band by any process to which it was subjected, it follows that urobilin is not the chief colouring matter of normal urine. Moreover, there is every reason to believe that the product obtained has not undergone any notable change in the process of extraction, although its solubility in various media appears to be somewhat impaired.

The question whether the yellow colouring matter so obtained is a definite chemical entity is one to which it is very difficult to give a conclusive answer, chiefly on account of its physical properties. However, the uniform course of events observed on each of the many occasions on which the alcohol and ether process was carried out, strongly suggested that the product was a definite compound.

This view also received support from its behaviour towards its solvents and its precipitation by ether, as well as by its effect upon uric acid crystals, which is hardly what might be expected from a mixture of pigmentary substances.

The only fact with which I am acquainted which appears to be opposed to this idea is the impossibility of completely decolorising its solutions by certain metallic precipitants, which throw down the * "The Influence of Colloi ls upon Crystalline Form and Cohesion," 1879, p. 52.

great bulk of the pigment; but, since we are ignorant of the form in which the pigment exists in such precipitates, i.e., whether it is in actual chemical combination with the precipitant, this objection does not appear to be insuperable, especially as other pigments, which are certainly definite compounds, appear to behave in a similar way.

There can, I think, be little doubt that the same substance formed the basis of the products obtained by Thudichum, Tichborne, Schunck, and myself, such differences as were observed being due to varying degrees of purity, and probably to changes produced in the pigment by the various methods of extraction employed.

The most important respects in which my product differed from the urochrome of Thudichum were its behaviour with ether and when heated with mineral acids.

The fact that ether, when shaken with normal urine, does not acquire any yellow tint suggests, but does not prove, that, in its original condition, the yellow pigment is insoluble in ether, and at no stage of my process is the product soluble in that medium. Urochrome, on the other hand, is described by Thudichum as being more readily soluble in ether than in alcohol. Again, a portion of Schunck's product (urian) was also soluble in ether.

I have myself found that the pigment obtained from urine by saturation with baryta, precipitation with the acetates of lead, and extraction of the precipitate with cold dilute sulphuric acid, followed by immediate neutralisation with ammonia, is to some extent soluble both in ether and in chloroform, and can only attribute this difference to a change produced by the process of extraction employed.

When acted upon by hydrochloric or sulphuric acid upon a water bath, my product behaved more like those of Schunck than like urochrome. The chief difference from Thudichum's results was that no portion of the residue was soluble in ether with a red colour. I should, however, mention that I have repeatedly obtained a substance yielding a rich red ethereal solution, when the specimens treated had not been freed from indoxyl sulphate, but never when this impurity had been got rid of.

To the difficult questions connected with the origin and formation, in considerable quantities, of a pigment, such as is here described, the source whence it is derived, and the manner in which it enters the urine, of which it is a constant constituent, it is, at present, impossible to venture even a hypothetical answer; and we may well content ourselves for some time to come with the attempt to establish upon a firm basis the contention that the yellow colour of urine is not due to any of the band-yielding pigments, but to a distinct yellow colouring matter, of negative spectroscopic properties, which may be judged from its reactions to be a definite chemical entity. For the designa

tion of this substance the name "Urochrome," assigned to it by Thudichum, appears eminently suitable.

The only points hitherto brought out which afford any clue to the chemical relationships of this pigment are the resemblance of the products of its decomposition to the humous substances described by Udránszky, and the fact that it yields, when heated with nitric acid, a colour reaction which is indistinguishable from the xanthoproteic reaction, suggesting a relationship to the members of the aromatic series.

Udránszky classes Thudichum's uromelanine and the other products of the decomposition of urochrome as humous substances, and suggests as a possibility that the conversion of carbohydrates into such substances begins even within the body, and so may contribute to the yellow coloration of urine.

Certainly uromelanine has, as might be expected, certain obvious resemblances to the products which Udránszky obtained by the action of acids upon urine, and Thudichum long ago described how it might be prepared directly from urine by similar means. On the other hand, even if it be granted that the yellow pigment does yield humous substances on decomposition, any argument based upon this may well be regarded as open to the objection of explaining ignotum per ignotius.

IV. "Some Points in the Histology of the Nervous System of the Embryonic Lobster." By EDGAR J. ALLEN, B.Sc. (London). Communicated by Professor W. F. R. WELDON, F.R.S. Received February 10, 1894.

The following observations have been made on late embryos of the common lobster (Homarus vulgaris) by means of Ehrlich's methylene blue method, as modified by Biedermannt and Apáthy. The results to be recorded in the present communication apply chiefly to the thoracic ganglia, which in the embryo are fused into one mass.

The nerve elements, which have stained, may be divided into three main groups—

I. Elements of which both the cell and the fibre lie entirely in the ganglionic chain, and which must be supposed to serve the purpose of co-ordinating the action of its various parts. *Zeitschrift. f. Physiol. Chemie,' vol. 11, 1887, p. 537, and vol. 12, 1888,

p. 33.

+ Biedermann, "Ueber den Ursprung und die Endigungsweise der Nerven in den Ganglien wirbelloser Thiere," Jena. Zeitschr.,' vol. 25, 1891.

6

Apáthy, "Erfahrung in der Behandlung des Nervensystems für histologischo Zwecke," I, Methylenblau. Zeitschr. Wiss. Mikr.,' vol. 9, 189