Abstract
After injection of acid fuchsin into the dorsal lymph sac of a frog and injury to the brain a marked absorption of the dye takes place followed by convulsions.
The absorbed acid fuchsin appears to be uniformly distributed throughout the entire substance of the brain and cord and in the quantities here employed it is always found to be present in these organs in the form of a colorless compound.
The decolorized acid fuchsin is found to be present in these tissues in so short a time as two minutes after the brain injury; the interval between brain lesion and convulsions may be somewhat longer.
The injury to the brain is considered to be the cause for the increased absorption of the dye.
In frogs with an intact cerebral nervous system we do not find absorption or only to a very slight degree (after injection of the dye in the quantities used above) and these frogs rarely show convulsions.
The occurrence of convulsions can not be explained by the increased absorption alone. Quite apart from this, the brain injury causes an increased disposition of the central nervous system to react with convulsions. A slight absorption of the dye in the intact brain is usually not followed by convulsions. We have no explanation to offer at the moment for this increased readiness of the central nervous system to react toward convulsive drugs of the type here studied but we have come to the conclusion that we are not merely dealing with the removal of inhibitory influences passing from the cortex to the subcortical centers.
The causes for the increase of absorption are not to be found in any alteration in the action of the heart or lymph hearts which results from the brain operation.
The acid fuchsin which comes into contact with the injured region, when blood containing the dye bathes this area does not enter to a marked degree the nervous substance at the injured place and does not spread out from there quickly into the other parts of brain and cord.
The dye which is contained in the spinal fluid (after bleeding has occurred) appears not to be absorbed by the substance of the central nervous system to any considerable. extent.
The conclusion is drawn that the brain injury causes an absorption of dye into the nervous substance directly from the blood vessels of the brain. It seems possible that the increased permeability of the blood vessels is caused by a change of the innervation of the blood vessels, but perhaps it is to be explained by a change in the condition of the nervous tissue (widening of perivascular and perineuronal spaces) or, finally the increased absorption of dye stuff may be due to a change in the pressure relations between the blood in the brain vessels and the tissue-fluid in the surrounding nervous substance.
The meninges in frogs protect the brain against the influence of certain crystalloid and colloid solutions brought into contact with their outside surface. Ten per cent sodium chloride solution, solutions of picrotoxin, strychnine nitrate and acid fuchsin put on the outside of the meninges cause convulsions only after the meninges have been cut open. Under these circumstances the acid fuchsin produces convulsions without brain injury because it is applied in high concentration. The convulsions in these animals probably are largely due to a direct influence of the acid fuchsin on the medulla oblongata., The presence of a region (Heubel's center) in the nervous structure of the posterior part of the medulla oblongata which controls motor impulses, is also made probable by the depressive effect of transection below the calamus scriptorius.
The brain injury is effective when done posteriorly to the fossa limbica, i.e., in the most anterior part of the cerebral lobes. Removal of the olfactory lobes is not sufficient. Removal of the optic lobes and of the anterior part of the medulla oblongata is also followed by convulsions. Slight prickings of the cerebral lobes, of the optic lobes and of the medulla oblongata have the same effect as the above mentioned removal of the anterior third of the cerebral lobes.
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