3rd. That the phosphoric acid is slightly increased in Dr G., and unaltered in quantity in J. W. P.

4th. That both of us lost weight slightly.

How can we explain these facts, which in every important point coincide in both of us. It is well known, that under various mental conditions the amount of urine is increased, and I have already pointed out, that if in health the urine be increased by drinking water, or by some static influence, the urea is also increased'. Now, under mental work it is the samegiven an increase of urine, an increase of urea is the result. The urea has no relation to the mental work except in so far as the latter influences the excretion of water. Under this perverted nervous action a general wash out takes place and the urea and chlorides are therefore increased.

In proof of this, if we look back to table VI. we find that on Feb. 24 there was a large excretion of water with increase of urea and chlorides; and again, while reading hard, from March 11th till March 13th, there was an increase in the quantity of urine, urea, and chlorides".

These experiments prove that the theory of the increase of phosphates in the urine under mental work is erroneous. In fact, it looks as if prolonged mental work rather decreased them, as if the brain during action did not only not lose phosphoric acid, but even required it for its action. If so, phosphoric acid has a similar relation to mental work, as nitrogen has to muscular work.

The loss of weight in both of us was due to more nitrogen passing off than the ingesta contained. This was especially so on the 29th, when the urine of both of us rose from some cause, and contained a very large amount of urea and chlorides; Dr Gamgee passing 104 grains of nitrogen more than his diet contained3, and J. W. P. an excess of 43 648 grains. This rise in the amount of urine and urea is so marked in Dr Gamgee's case that this day has not been included in the calculations, as

1 See p. 288 for the effect of water. See also Dr Smith's Paper in the Proc. Roy. Soc., London, May 30, 1861, "On the influence of Barometric pressure and temperature on the excretion of Urine."

2 See Table VII. p. 306.

3 Compare Tables X. XI. XIII.
4 Compare Tables IV. XII. XIII.

it immediately preceded the work period, and would most probably have falsified the results; and because late in the previous evening and during the early part of the night his brain was in an unusually active condition.

PART IV.

ON THE PHYSIOLOGICAL RELATIONS OF UREA.

Until lately the old theories of the production of urea from excess of nitrogenous food, and oxidation of muscle, muscular force resulting from that oxidation, were believed.

In 1866, Professors Fick and Wislicenus', from the results of their experiments on ascending the Faulhorn on a purely non-nitrogenous diet, concluded that the nitrogenous parts of muscles do not waste during action, and that urea is not the measure of intra-muscular changes during action. Since then Dr Parkes has corroborated their view, that the evolution of nitrogen is not a condition of muscular action. Their experiments tend strongly to support the theory that muscular force is derived from the oxidation of hydro-carbonaceous materials in muscle, and Dr Frankland's experiments on the amount of potential energy in various articles of diet corroborate this, for he found that the amount of energy stored up in hydro-carbonaceous substances was much greater than that in the nitrogenous. If, then, urea does not proceed from the oxidation of muscle, whence does it come?

Zalesky, having denied the presence of uric acid in the blood of birds, Meissner, from analyses, proved its presence in that fluid, and as he found it in much larger proportion in the liver than in any other tissue, obtaining as much as 31 grm. from 500 grms. of liver, he gave it as his opinion that uric acid was formed in the liver.

1 On the origin of Muscular Power, by Dr A. Fick and Dr J. Wislicenus, Zurich. London, Edin. and Dub. Phil. Mag. 1866, p. 485.

2 Proc. Roy. Soc. Lond., Vol. xvi. p. 44.

3 Lond. Edin. and Dub. Philosph. Mag., Sept. 1866.

4 Centralblatt, 1865, p. 202. Journ. Anat. and Phys., Vol. III. p. 239.

5 Henle und Pfeuffer's Zeitschrift, 13, xxxI. pp. 144-223. Journ. Anat. and Phys., ut supra.

Formerly it was stated by Heynsius and Stokvis that urea existed in the liver1, and Meissner has now shown that it exists in the livers of both the carnivorous and herbivorous animals in much larger proportion than was believed, obtaining as much as '09 grm. from 474 grms. of dog's liver, and 025 grms. from 347 grms. of rabbit's liver. He therefore advanced the theory that urea is formed in the liver, and he is supported by the following facts:

1. It has never been found with certainty but in the liver, blood and urine.

2. Frerichs and Städeler state, that in the urine of acute yellow atrophy of the liver the urea is not to be found, its place being taken by leucine.

3. Again, Harley has failed to detect it in cases of chronic atrophy of the liver3.

4. Vogel states that it is diminished in carcinoma of that

organ.

5. In some cases, where the liver is much disordered with fœtid high-coloured urine and no febrile state of system, urea is increased.

These facts undoubtedly point to the liver as being the factor of urea, and it seems reasonable to suppose that so large and important an organ should have some other function than merely to excrete a few ounces of bile daily. That other function has been already in part known as its glycogenic function". I say in part, for it is only now that another part is known.

It was long known that the liver of animals fed entirely on animal food, secreted sugar. Now, as animal food contains no starchy elements from which that sugar could be formed, it was argued, and then proved by experiment, that the liver had the power of making sugar. Bernards, supported by Lehmann®, believed that the sugar was formed from albuminous compounds, because there was less albumen in hepatic than in

1 Journ. Anat. and Phys., ut supra, p. 240.

2 Clinical Treatise on Diseases of the Liver, by Dr Frerichs, Vol. 1. p. 220. New Sydenham Soc. Edition.

3 Prin. of Human Physiology, Carpenter, p. 463.
4 Bernard, Archives Générales de Médicine, 1848.

5 Op. cit.

Carpenter, op. cit. p. 436.

6 Carpenter, op. cit. p. 436. Compt. Rendus de l'Acad. des Sciences, 1855,

p. 587.

portal blood, and they thought that the albumen was split up in the liver into the sulphuretted biliary acids and sugar. Then, however, the old theories of the production of urea were held. Now they are known to have been wrong. If the liver form bile and sugar, two hydro-carbonaceous substances the former containing only a very small per centage of nitrogen-out of highly nitrogenised albuminous compounds, what becomes of the 15 per cent. of nitrogen? It goes to the formation of urea, urea being formed in the liver from the splitting up of albumen. Whether it be at once formed or only produced after many changes, is at present unknown. The latter is the more probable1. Schultzen and Neubri of Berlin2 believe that it passes at least through leucine and glycocol, and in animals whose urea excretion is constant, they have found that the increase of urea is in exact proportion to the amount of glycocol given with their food.

The albuminates contain 15'4 Grms. 237'65 grains of Nitrogen.

=

The albuminates, carbohydrates and fats contain 208 633 Grms. = 3219 624 grains of Carbon.

=

1 See the decrease in the amount of uric acid from taking water, p. 288 and Table VII.

2 Academy, Jan. 8, 1870.

The albuminates contain 13.3 grms. = 205 245 grains of Nitrogen. The albuminates, fats and carbohydrates contain 186 61 grms. = 2879 78 grains of Carbon.

Total in grms. 2161.9 461.1 97.79 273:44

76 206 14.66

The albuminates contain 15'52 grms. =239'5 grains of Nitrogen. The albuminates, fats and carbohydrates contain 223 926 grms. =3455 grains of Carbon.