Electrical Impedance Changes of the Cat's Foot Pad in Relation to Sweat Secretion and Reabsorption

Impedance across the cat's foot pad, the glands being at rest, has a high quite constant value in a given preparation. Stimulation of the sudomotor nerves causes a decrease to a low constant value. After cessation of stimulation impedance returns slowly over a course that is linear with respect to the logarithm of time. The resistive and capacitative components vary with each other. Sweat reabsorption during recovery progresses linearly with respect to time. Hence impedance varies as the logarithm of reabsorption, and therefore as the mean level of sweat columns in the ducts. This relation can be accommodated by supposing that the sweat duct epithelium resembles a core conductor. An electrical model constructed on this principle is shown to behave as does the foot pad. During stimulation at a fixed frequency impedance change varies as the logarithm of duration showing that the amount of sweat produced per impulse at a given frequency is a constant. With frequency of a fixed number of stimuli varied the impedance change varies with it in a manner consistent with the view that the amount of sweat produced per impulse is a constant regardless of frequency.     

The production of ryegrass labelled with carbon-14

Summary The construction and operation of a growth chamber for producing plant material labelled with carbon-14 to a specified degree of uniformity is described.The specific activity of the plant material is measured by a method based on scintillation counting.     

The use of thin soil sections for the study of soil micro-organisms

Summary Modifications of Alexander and Jackson's¹ technique for the preparation of thin soil sections are described.The distribution of bacterial colonies within soil aggregates has been examined using this technique and it has been demonstrated that distinct distribution patterns may occur.