The only part of this statement not conceded today is that relating to the formation of internal secretions by tissues other than those of which the cells are definitely glandular, that is secretory:  as can be determined under the microscope.  Brown-Sequard added to the concept of internal secretions, fathered by Claude Bernard, the idea of a correlation, a mutual influencing of them and of the different organs of the body through them.  The nervous system had hitherto been regarded as the sole means of communication between cells, by its telegraphic arrangements of nerve filaments reaching out everywhere, interweaving with each other and the cells.  The Brown-Sequard conception inferred the existence of a postal system between cells, the blood supplying the highway for travel and transmission of the post, the post consisting of the chemical substances secreted by the glands.  To be sure, the doctrine was only an inference, though well-founded, of which the direct experimental proof was not to be obtained until the researches of Bayliss and Starling.  Yet to Brown-Sequard belongs the immortal credit, if not of the originator, at any rate of the resurrector of the idea of using gland extracts to influence the body.  The unwarranted hopes aroused by his enthusiastic reports of rejuvenating miracles have long since been dissipated.  Moreover, they smeared the whole subject with a disrepute which clings to certain narrow and unreasonable minds to this day.  But as every physiologist since has acknowledged, he was and remains the great path-breaker in the conquest of the internal secretions.

THE HORMONES

The problem of the internal secretions was now attacked from another angle.  A great Russian physiologist, Pawlow, called attention to the fact that the introduction of a dilute mineral acid, such as the hydrochloric acid, normally a constituent of the stomach digestive fluid, into the upper part of the intestine, provoked a secretion of the pancreas, which is so important for intestinal digestion.  He explained the phenomenon as a reflex, a matter of the nerves going from the intestine to the pancreas.

His pupil, Popielski, threw doubt upon so easy an explanation, by proving that the same reaction could be elicited even after all the nerve connections between the gut and the spinal cord were severed.  If the relation was a reflex, it would have to be classed now as one of those local nerve circuits, which are pretty common among the viscera, a local call and reply as it were, without mediation of the great long distance trunk lines in the spinal cord and the medulla oblongata.