26 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS permeability of frog skin increased after treatment with aluminium salt astringents. The complete antiperspirant product was applied to the dorsal skin of frogs 1 h later skin samples were removed and the extent of iodide penetration from a radio-active solution was determined. In vivo methods Cats (16-19), rats (19-21), and mice (21), have been used for studies of sweating, but the sweat glands in these species are confined to the foot- pads and although they are eccrine glands they differ histologically from those of man. In vivo studies involving the human eccrine sweat gland system are obviously preferable and investigation of all aspects of sweat glands and their function has resulted in a variety of techniques for visual- izing, assessing and collecting sweat. Some of these methods are purely qualitative, others are quantitative or semi-quantitative. Stimulation of eccrine sweat glands for experimental studies Excitation of the glands is a prerequisite of studies on sweat gland function since the resting secretion is small and consequently difficult to measure under such conditions inhibition would be even more difficult to assess. Stimulation has been achieved by administration of 0.5-1.0 g acetyl- salicylic acid, followed by the intake of copious quantities of hot tea (22). More recently, injection of cholinergic compounds such as acetyl choline, mecholyl, carbachol, or pilocarpine (23, 24) has been found to induce sweating, and is frequently used in sweat gland studies. Although exercise and application of local heat (23) promote a response, one of the most useful methods of inducing sweating is to place the subject in a warm room, or chamber (23, 25-28). Recommendations of different authors for values to be maintained in such a room vary considerably, but generally are within the range 32-40øC and 40-80% relative humidity. Studies of axillary perspiration are most conveniently carried out under such conditions. After entering a warm environment there is generally a latent period before perspiration increases (29) and so the subject is allowed to reach equilibrium with his surroundings before measurements are taken.

MEASUREMENT AND CONTROL OF PERSPIRATION 27 VISUALIZATION OF SWEAT AND THE SWEAT DUCT ORIFICE Colorimetric techniques Although the presence of sweat can be observed with the unaided eye, or by use of an otoscope or dissecting microscope {S) determination of the numbers of sweat glands and semi-quantitation of sweat is more readily carried out if use is made of a chemical reaction involving a colour change. The intensity and extent of the colour change provides an indication of the amount of sweat produced. In these methods the solutions are painted directly on to the skin and solubilization of the reagents by sweat effects a colour change. The well-known starch-iodine test devised by Minor in 1027 {22, 30) was one of the earliest colorimetric methods and gave blue-black coloration at the site of sweating. Since then there have been modifications of the method (31, 32) which permits extremely small quantities of sweat to be seen with the naked eye. In place of iodine Guttmann {33) used the sodium salt of chinazarin 2-6-disulphonic acid. Comparison of the effects of different treatments on the same group of glands has been achieved by preparing black and white positive trans- parencies from photographs of the treated site {visualized by the starch- iodine method) and then superimposing these transparencies {34). Other indicators used have been saturated alcoholic cobalt chloride which gives a colour change from blue to bright pink (35), phenolphthalein which goes deep red in contact with sweat (36), a suspension of bromo- phenol blue in silicone (37), and a 5% solution of o-phthaldialdehyde in xylene which gives a black stain when it comes into contact with the ammonia present in sweat (38). Although most of the stains used in these procedures can be washed off the skin, some of them are more permanent and several workers have adapted the starch-iodine method, or devised other methods, which allow the colour reaction to develop away from the skin. These methods have the added advantage that they provide 'prints' of the sweat pore pattern and can be used on dark-skinned subjects. Randall (23) used iodine on the skin in conjunction with a starch-containing paper Papa (39) exposed a paper towel to iodine yapours after it had been in contact with skin painted with a starch-castor oil mixture. Silverman and Powell (40) reacted a 25% solution of ferric chloride, painted on the skin, with a paper which had been soaked in 5}/0 tannic acid