Description: Segment 1 Chayen starts his lecture by describing what hormones do. He calls them chemical messengers, produced by one cell type, carried through the blood to its target cell where it changes or regulates the metabolic activity of those target cells. Using an animated illustration of the human body, Chayen shows which areas of the body different hormones originate and where there target cells are most likely to be he also shows a graph detailing the different levels of various hormones likely to be found in the blood. Chayen then introduces the new technique of microbioassays these depend on a form of cellular biochemistry known as cytochemistry which measures the biochemical changes produced in each cell in a hormone's target. Time start: 00:00:00:00 Time end: 00:05:22:00 Length: 00:05:22:00 Segment 2 Chayen narrates over a very detailed filmed demonstration of the preparation and making of a cytochemical bioassay. After preparing the adrenal glands from a guinea pig, a series of culture mediums are prepared and applied to samples of the adrenal gland tissue. When the samples are ready, they are cut into sections of 10 microns. Time start: 00:05:22:00 Time end: 00:11:00:00 Length: 00:05:38:00 Segment 3 Chayen continues to narrate over the filmed demonstration of a cytochemical bioassay taking place. He shows how the tissue samples are cut. Each sample can be tested for its reaction to a specific hormone - Chayen lists a great many of these reactions. At this point he introduces the technique of microdensitometry which enables the density of microscopic areas to be measured. A film of this technique is shown and Chayen describes, in detail, how it works and how it is best adapted to the purpose of measuring hormones. Readings from the microdensitometer are shown plotted in a graph and Chayen explains what they mean. Time start: 00:11:00:00 Time end: 00:19:28:20 Length: 00:08:28:20 Segment 4 Chayen acknowledges that it is very difficult to measure low concentrations of hormones. The answer, he says, is to measure the initial rate of a chemical response because if that rate were maintained within the human body it would produce a physiological effect. He explains this process further in relation to various hormones, particularly ACTH (adrenocorticotropic hormone), and he shows graphs detailing the results of cytochemical bioassays on these hormones. Time start: 00:19:29:00 Time end: 00:25:16:00 Length: 00:05:47:00