the ossific matter was about half the size of the cerebrum, and weighed fourteen ounces. But the particular case to which the title of Vallisnieri's book alludes, according to Haller (Bibliotheca Anatomica, tom. i, p. 792), was not a true ossification of the cerebrum, but an exostosis. Swedenborg, also, mentions an ossified brain found in Sweden, and preserved in the collection of Bromellius, and which is treated of in the Acta Upsaliensia.

THE CHANGES PRODUCED ON STARCH DURING DIGESTION.

By Dr. R. D. THOMSON, Glasgow.

As starch, or substances allied to it, constitutes the basis of the food of many of the animals that come under the care of the veterinary surgeon, the following experiments will not be read without interest :

"As it appeared to be a matter of importance in the investigation of the changes occurring in the stomach during digestion, in order to prevent complication of the phænomena, that the food should be as simple as possible, I have chosen for the experiments about to be detailed cases in which animals were fed on vegetable food alone. In general, the species of food selected was porridge, or a mixture of oatmeal and water well boiled. In such experiments as I have seen detailed, in reference to the free acid of the stomach, there appears to have been too little attention paid to the possible results which might arise from a difference in the nature of the food thus the products of the digestion of starch we should naturally expect to be different from those of the digestion of animal fibrin or albumen, since we know that lactic acid can be produced by a modification of starch, although the same change does not attend the decomposition of the animal substances enumerated. For example, in the preparation of starch an acid liquor collects on the surface of the vessels in which the starch is digested, and in the formation of sowans from oat-husks and water by steeping, an acid liquor is developed-in both instances a consequence of the production of lactic acid at the expense of starch; while in the German dish, saurkraut, the same acid is

generated by an analogous action. I do not at present intend to discuss the nature of the acid which presents itself in the stomach during the digestion of animal food, but simply to detail the results of a series of experiments upon the changes produced on vegetable food and starch during digestion. I shall merely content myself with stating, that I have never found a volatile acid in the stomachs of animals which were digesting animal food alone, while in these cases I have invariably found an acid to be present which was fixed at the temperature of 212°, and even considerably higher.

The nature of the acid developed during the digestion of Starch.It does not appear an invariable rule that an acid reaction should always characterise the liquid present in the stomach during digestion, as appears from the following experiment:-On the 11th of July 1844, the different stomachs of a sheep killed twentyfour hours after partaking of grass, contained between two and three pounds of finely-divided green matter, exhibiting a pulpy consistence, but being entirely destitute of either an acid or alkaline reaction. The pulpy masses were tested in each of the stomachs with the same negative result, and they were afterwards mixed together, diluted with distilled water, and filtered, but still without producing any effect on litmus paper. Experience teaches us, that, to determine the presence of a volatile acid in the stomach, great care must be taken in reference to the mode in which the distillation is performed; since if the heat of an open fire is applied to the retort, an indication of the presence of hydrochloric acid will be found in the liquid contained in the receiver by the addition of nitrate of silver. The following experiment affords evidence in favour of this position, and it might be strengthened, if necessary, by the results obtained by other experimenters. The contents of the stomach of a dog which had been fed on porridge made of oatmeal and water, and which afforded an acid reaction with litmus paper, were mixed with distilled water, and filtered. On exposing the distilled liquor to the heat of an open fire in a retort, a fluid passed over, possessing an acid reaction, and becoming opalescent on the addition of a solution of nitrate of silver, and without this appearance in contact with nitric acid; a result plainly indicative of the presence of chlorine in some form

in the liquor of the receiver, but, as appeared by the subsequent inquiries, to be explained by the fact that muriate of ammonia must have been carried over by the vapour of water in consequence of the excess of heat.

"To determine in a satisfactory manner, therefore, the presence of a volatile acid, it is necessary to distil the fluid contents of the stomach in a water-bath. With this consideration in view, the following experiment was made :-June 1844, a pig was fed on potatoes and greens, and was killed in half an hour after the food was swallowed. The stomach was slit open, and as much of the fluid contents as possible were poured off; the solid contents were then digested in cold distilled water. Both fluids were filtered and mixed, each, previous to being united, being found to exhibit an acid reaction with litmus infusion. To ascertain whether the statement made by a French physiologist (Blondlot) is correct,-viz., that the acid of the stomach cannot be saturated with chalk,—a quantity of pure carbonate of lime was prepared by dissolving Irish limestone in hydrochloric acid, precipitating a small portion of phosphate of lime and iron which it contains with caustic ammonia, and then throwing down the lime with carbonate of ammonia, collecting the precipitate on a filter, washing it well with distilled water, and heating it to redness in a platinum crucible. An excess of this chalk was then added to the filtered fluid of the stomach, and the mixture was allowed to remain for twenty-four hours, disturbed only by frequent agitation. It was then filtered, and found to have been completely neutralized. Having often repeated this experiment on various specimens of gastric fluid with the same effect, I can only account for the different result obtained by Blondlot, by supposing that he had attempted to complete his neutralization of the fluid while it was in a heated state; and that possibly, if acetic or lactic acids were present, these acids might resist neutralization at an elevated temperature, since it has been found by manufacturers of pyroligneous acid that they cannot succeed in forming a neutral acetate of lime at a temperature approaching that of the boiling-point by chalk alone, but that they require to add milk of lime in order to overcome the acid reaction. Blondlot has deduced the inference from his experiment, that the stomach owes its acid reaction to the presence of

an acid phosphate of lime; but as the experiments now detailed do not coincide with those of the French physiologist, it is sufficiently obvious that they do not support him in his conclusions.

Being thus foiled in corroborating the deduction of Blondlot, that phosphoric is the free acid of the stomach, it was requisite to look out for another source of the acidity of the gastric fluid: it was therefore necessary to test the muriatic or hydrochloric acid theory, as propounded by the sagacity of Dr. Prout. (See Philosophical Magazine, S. 2, vol. iv, pp. 3 and 120.)

"The contents of the stomach of a pig, which had been fed on porridge two hours before being killed, were mixed with cold distilled water, and filtered. Six ounces of this fluid, which was quite clear and limpid, were introduced into a retort, and distilled in a water-bath. The distillation occupied several hours; three ounces of fluid were distilled over, which possessed the peculiar smell of such fluids, and reddened infusion of litmus slightly. The three ounces of fluid remaining in the retort had a strongly acid reaction, and gave no appearance of acetic acid on the addition of chloride of iron. From twelve ounces of another portion of the same gastric fluid four ounces of fluid were distilled over by the heat of the water-bath, which presented the same characters as those of the distilled fluid just described; but in neither instance could a trace of hydrochloric acid be detected by nitrate of silver.

"With the liquor remaining in the retort, three experiments were made to determine the possible amount of free hydrochloric acid, on the supposition that the preceding experiment did not serve as evidence to prove the impossibility of its presence. Three equal portions of the fluid were measured out, to the extent of two fluid ounces in each portion.

"1. To the first portion a solution of nitrate of silver was added until a precipitate ceased to fall; pure nitric acid was then mixed with the liquid, and the temperature raised to the boiling point. The precipitate was filtered, washed, and weighed.

"2. The second portion was evaporated to dryness, and ignited; the residue was dissolved in water and precipitated by nitrate of silver, the solution being acidulated with nitric acid and brought to the boiling point.

"3. The third portion was exactly neutralized with caustic potash,

evaporated, and ignited; the residue dissolved in water, and the solution precipitated by nitrate of silver.

"The results of these experiments are indicated in the following

The atomic weights here employed are Dr. Thomson's :—

"The correspondence between the first and third experiments. shews that in the first no organic substance had been in union with the silver, which was precipitated by chlorine alone, and that there is no evidence from these results of free muriatic acid being present. The conclusion is the reverse, since, if any free muriatic acid had been neutralized by the potash, the third experiment ought to have given an inferior quantity of chloride of silver, because the salammoniac ought to have been sublimed. The potash which was added, I conceive, in the third experiment, united with an organic acid the salt formed was decomposed by the incineration, and the potash united to the chlorine previously in union with ammonia; for that sal-ammoniac or a volatile muriate was present is proved by the second result.

"It is well known that Dr. Prout, by similar experiments, drew the conclusion, that free hydrochloric acid was present in the stomach. That distinguished chemist, however, omitted the first . experiment which I have described. Indeed, he could not have made it successfully under the circumstances in which he operated, because the gastric juice in his experiments was not exposed to a heat that could coagulate and separate the albuminous matters, which would then have combined with the oxide of silver, and have complicated the result. In the gastric juice employed in the preceding researches, however, nothing was present but soluble starch or dextrin and sugar, which formed obviously no compounds