A model is developed for the regulation of temperature in man. The thermal properties of the body are presented in circuit form and simplified to eliminate all features not essential to an understanding of control. In this modeling, perspiration is treated as a source which can pump heat against a temperature gradient while lung heat loss appears as a high-frequency alteration in effective heat production. To this simplified thermal circuit are appended the principal mechanisms which are available to the nervous system for controlling body heat balance-increased metabolism as in shivering, increased heat loss by perspiration, and alteration of thermal conductance through changes in blood flow-and a block diagram of the resulting control system is given. The description of these mechanisms follows that of Benzinger and co-workers Benzinger & Benzinger, Pratt & Kitzinger, 1961.

A mathematical model, explaining the adaptation commonly seen in the response of amphibian muscle spindle receptors to sudden increases in muscle length, is developed. It is shown that interaction between supposed mechanical properties of the reticulated and dense zones of intrafusal fibers could be the sole source of this adaptation. The model also displays the characteristic response of spindle receptors to intrafusal motor stimulation. The validity of this model appears easily tested.