| Popis: |
1. A historical survey of the subject is presented. 2. Possible explanations of the divergent results of previous workers are given. 3. A new type of electrode which I have evolved for this class of work is described. 4. Original observations on the action of thyroid preparations are presented, from which the following conclusions may be drawn:- a. Injection of thyroid extract invariably produces a fall in the bloodpressure in cats and dogs. This may or may not be accompanied by an alteration in the heart rate. b. More than one substance is responsible for this depressor effect all of which are readily hydrolysed by alkali, to substances having physiological properties similar to those of trimethylamine. c. The injection of thyroid extract has no definite and specific effect which is demonstrable in the course of an "acute" experiment, upon the response to subsequent stimulation of the cardiac fibres of the vagus in the cat. d. Injections of extract of liver or of tonsil may be followed by effects upon the cardio -vascular nerves, similar to those succeeding thyroid extract. e. These phenomena may also occur after the injection of Lockets solution, or may appear apparently spontaneously. f. Thyroxin has no definite and unmistakable effect upon the cardio -vascular system, demonstrable in an "acute" experiment. g. No support can be given to the statement that the injection of thyroid extract, or of thyroxin, increases the response to subsequent injections of adrenalin. 5. There are indications throughout these experiments which suggest that the minimal stimulus to be applied to the vagus in order to produce cardiac inhibition in the cat, varies in strength between wide limits. 6. Further investigation into the conditions affecting the excitability of, and the onset of fatigue in, the cardio-inhibitory fibres of the vagus, is indicated. |
