We studied the absorption capacity of the upper small intestine using the following tests:1. Potassium iodine test. 20 ml of a 2% solution of potassium iodide is injected intraduodenally and every minute its presence in saliva is determined using the iodine-starch reaction.2. Samples with radioactive iodine. 2 μ curie Nal ¹³¹ is injected into the duodenum and the absorption of radioiodine by the thyroid gland is recorded within 15 minutes.3. Ether test. The moment of feeling the smell of ether from the respiratory tract after the intraduodenal administration of 1.5 ml of ether in saline is noted (N. Benda test, 1954).