Facts such as these have been long held adequate to prove that some poisons must act on remote organs by sympathy or transmission of a local impulse along the nerves; and in the last edition of this work they were acknowledged to warrant such a conclusion. It was thought difficult to account for the phenomena on the supposition that the poison was conveyed in substance with the blood to the organ remotely affected by it; for it appeared impossible that, in so short a space of time as elapsed in some of the instances now referred to, the poison could enter the veins of the texture to which it was applied, pass into the right side of the heart, follow the circle of the pulmonary circulation into the left side of the heart, and thence be transmitted by the arterial system to the capillaries of the organ ultimately affected. But the progress of physiological discovery has lately brought the soundness of these views into question. Some years ago Dr. Hering of Stuttgardt showed that the round of the circulation may be accomplished by the blood much more speedily than had been conceived before; for the ferro-cyanide of potassium, injected into the jugular vein of a horse, was discovered by him throughout the venous system at large in the short space of twenty or thirty seconds, and consequently must have passed in that period throughout the whole double circle of the pulmonary and systemic circulation.[16] This discovery at once shook the validity of many, though not all, of the facts which had been previously referred to the agency of nervous transmission on the ground of the celerity with which the effects of poisons are manifested. More recently an attempt has been made by Mr. Blake to prove, that the circulation is so rapid as to admit even of the swiftest cases of poisoning being referred to the agency of absorption. Mr. Blake, who is altogether opposed to the occurrence of nervous transmission in the instance of any poison, has found that ammonia, injected into the jugular vein of a dog, was indicated in its breath in four seconds; and that chloride of barium or nitrate of baryta, introduced into the same vessel, could be detected in the blood of the carotid artery in about sixteen seconds in the horse, in less than seven seconds in the dog, in six seconds in the fowl, and in four seconds in the rabbit.[17] These interesting discoveries, however, will not absolutely destroy the conclusiveness of all the facts quoted above in support of the existence of a sympathetic action. For example they do not shake the validity of those observations, in which it appeared that an interval inappreciable, or barely appreciable, elapsed between the application and action of hydrocyanic acid and of conia. Mr. Blake indeed denies the accuracy of these observations, insisting that, in those he made himself with the most potent poisons, he never failed to witness, before the poison began to act, an interval