common Resin, which consists of two isomeric acids, Pinic

C20 H16+30=C20 H15 O2 + HO.

or, Oil of Turpentine, with the addition of three atoms of Oxygen, produces Pinic acid, i.e. Resin, and an atom of water. Turpentine, when given in large quantities, irritates the surface of the intestinal canal in man, and is not absorbed. But in the horse very large doses are found to pass through the system into the urine. It is not likely that a large quantity should enter in solution in water. It seems more probable that it may first in some way become oxidized, and then dissolved as a resin. The action of turpentine resembles that of some other substances which contain resin, as Copaiba and Balsam of Peru.

The resins thus dissolved would pass, like other solutions, through the mucous membrane of the intestines into the Portal capillaries.

But of the fats and fixed oils it cannot be said to be proved that they are absorbed in a state of solution, although such a conclusion is almost forced upon us by a consideration of the laws of endosmosis. They do not pass into the veins, but are taken up by the lacteal absorbents. They are capable of solution, and are thus not in that sense an exception to the rule of Prop. II. But in another sense they are an exception to it; for they do not pass directly into the veins, but through the lacteal system. It seems that the chief or sole purpose of these lacteal vessels is to absorb fats. Thus it appears that all soluble substances, whether in the food or given as medicine, and in whatever manner rendered soluble, whether by acid, by alkali, or by stomach digestion, are absorbed in the stomach and intestines. All of them, with the exception of fatty mat

ters, pass directly into the blood, traversing the mesenteric and Portal veins, to reach the liver. From this organ they pass on into the heart through the Vena cava inferior. I have shown also that they are mostly absorbed without material change. Supposing the stomach acid to be lactic, it would be too weak to displace mineral acids. It would however decompose a few insoluble matters, and combine with alkalies and their carbonates, forming salts which in the blood would again change into carbonates. (Vide Prop. VI.)

PROP. III.-That those medicines which are completely insoluble in water, and in the gastric and intestinal juices, cannot gain entrance into the circulation.*

It may at first sight be objected to this proposition, that fatty matters may probably enter the lacteals in an undissolved state. But this is not proved; and besides, whether dissolved or not, we know that they are soluble in one at least of the intestinal juices-viz. the Bile. So that they do not come under the above definition.

We have just seen that many medicines which are given in the insoluble form are capable of being dissolved in the fluids of the intestinal canal. This so much reduces the list of perfectly insoluble medicines, that it is difficult to find any that come under such a definition. But Charcoal, the simple metals, woody fibre, and Nitrate of Bismuth, will serve as examples.

Sulphate of Lead is often quoted as perfectly insoluble ; but this is not the case. It is soluble in a solution of Acetate of Ammonia. This salt is contained in the perspiration. Thus the sulphate, when substituted for the carbonate in some lead works at Paris, proved fatal to the foreman, who died of colic. M. Flandin found that it poisoned a dog when rubbed into the

"The remedy must be soluble, or capable of becoming so, in the fluids of the living body, before it can be absorbed.”—Mialhe, op. cit.

G

skin as ointment. Even some metals may possibly be brought within the influence of weak acids when in a fine state of subdivision, as Mercury in blue-pill. Gold in a very fine powder has been used successfully in syphilis.

Thus the list of insoluble substances is still further reduced. But there is no doubt that many substances which are slightly soluble in the intestinal fluids may in great part escape this solution, and pass out with the fæces just as they went in.

To assert that the particles of an insoluble substance cannot pass through the homogeneous wall of the capillary or absorbent vessels, is merely to state what follows from an absolute physical law, and is generally admitted by physiologists. But even this fundamental datum has been lately attacked.

Professor Esterlen of Dorpat has been induced to affirm the possibility of the absorption of insoluble substances, from some experiments which he has made. Finely-powdered charcoal was administered to rabbits for some days. They were then killed, and globules of charcoal, measuring from to 3000 of an inch, were found in the blood of the Portal circu

* Dr. A. Fleming, in an article in the British and Foreign Medical Review,' quotes Matteucci as stating that the interstices of the animal tissues vary in diameter from too of an inch. He then asks, What is to prevent minute particles of charcoal from passing through such openings? Surely there is here some terrible mistake! Matteucci is speaking of such interstices as those between muscular fibres, or in the meshes of areolar tissue,—and the reviewer applies the statement to the membrane through which the absorbed particles must pass. This is well known to all physiologists as homogeneous or basement membrane. I need hardly remind the reader that no apertures whatever can be discovered in this membrane, even by the highest power of the compound microscope. So that unless this membrane underwent some lesion or injury, no particle large enough to be seen through such a microscope could pass through it without being first dissolved. But every substance absorbed in the intestinal canal must pass through at least two layers of this membrane, one belonging to the mucous coat, the other constituting the delicate wall of the capillary vessel.

lation.* (Zeitschrift für Rationelle Medizin, 1847.) To obtain these results the microscope was used, a far less certain test in such matters than chemical analysis. Esterlen reasonably concludes that, if charcoal can so pass, so also can any other insoluble substance. The necessity of solution could then at once be done away with, and the blood continually liable to admixture with all kinds of heterogeneous and crude materials. Esterlen asserts further that he has found minute globules of mercury under the skin after rubbing in mercurial ointment. (Journal für Praktische Chem., No. IX. 1850.) Now, if these things were true, there could be no need to suppose the solution of insoluble active medicines, for they would be enabled without difficulty to pass through in an undissolved state.

I have therefore repeated the above-mentioned experiment of Esterlen, taking every precaution that I could think of to guard against a fallacy.

Half a pound of highly purified and finely powdered animal charcoal was triturated for some time with water, in order still further to increase the tenuity of the particles. Some of this paste being then examined under the microscope, and the particles carefully measured with the spider-web micrometer, their size was found to average of an inch, some being much smaller, others larger. This charcoal paste was now administered, in divided portions, during seven successive days, to three rabbits and a guinea-pig, being mixed up with the pollard which was given to them as food. At the end of this time, no morbid or other symptom having been observed, except the carbonaceous character of the fæces, they were killed by Prussic acid. On opening them, a blackening of the inner surface of the stomach and intestines was the only

* It will be observed that the largest of these are just equal to the average size of the corpuscles of the blood. So if the particles of charcoal passed into the vessels, why did not the blood corpuscles pass out? Vessels having walls pierced with such apertures as to allow of the entrance of these bodies, would probably permit of copious and continual hæmorrhage. For it is well known that blood corpuscles will pass readily, by undergoing compression, through passages of a much less diameter than themselves.

peculiar appearance noticed. Specimens of the fresh blood of each were then successively examined under the microscope, the blood being taken from the right cavities of the heart, the Portal and mesenteric veins, and the inferior vena cava. An 8th of an inch object-glass was used. In the majority of cases nothing at all was seen except the blood corpuscles. But in about one out of four observations first made, some amorphous black particles were perceived, the appearance of which was at first dubious. They were very few in number-only one or two among myriads of blood corpuscles-and they would not have been noticed at all had it not been for the peculiarity of the investigation. Their size at once excited suspicion, some of them measuring six times the diameter of a blood corpuscle (3 of an inch). In fact, they were found to be minute particles of dust, and they were only got rid of by the most assiduous attention to the cleaning and protection of the glasses in subsequent observations. Besides these, there was now and then seen an amorphous molecule of hæmatine, such as is known to occur occasionally in healthy blood, especially that of the splenic and Portal veins. Such particles are known by their partial translucency, and the possession of a yellowish or brownish colour.

I thus saw no appearance which could be at all compared with the observations of Esterlen, who describes particles of charcoal as occurring in abundance in blood drawn from each of the four sources just mentioned.

To test in another way the accuracy of the above observations, I killed two cats, which had been for some time fed upon milk, at King's College. I then examined their blood in the same way. I found, in several instances, the same solitary hæmatine globules, and experienced the same difficulty as before in getting rid of stray particles of dust. It is quite clear that in animals fed on milk, these latter could have had no connection whatever with the passage of charcoal from the intestinal canal into the blood.

It may still be asked of me, how I would explain the recorded observations of Esterlen. It is very likely that they are not altogether inaccurate. It has occurred to me that they may possibly be accounted for by supposing that in the animals which he fed upon charcoal, the irritation might have been sufficient to establish some minute points of ulceration by means of which there would be a communication between the intestine and the cavity of the vessel, sufficient to allow of the passage of the carbonaceous particles, without permitting any notable hæmorrhage (though this last is difficult to believe). Thus, in the black phthisis of colliers, it is supposed by some pathologists that the sooty matters inhaled find their way into the blood through ulcerations in the walls of the air-cells.