24 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS their own duct orifice (2). Spearman (3) has demonstrated that a minority of eccrine glands are twin glands with a common terminal excretory duct. Functional from the age of 2« years, the eccrine glands are distributed over the whole body surface, and are concerned with the regulation of body temperature by the evaporation of sweat from the skin surface. Eccrine secretion is a clear fluid (pH 4.0-6.0) consisting of 99.0- 99.5% water and 0.5-1.0ø//0 solids, a mixture of inorganic salts, largely sodium chloride, and organic substances which include lactic acid and traces of urea (4). Apocrine sweat glands The apocrine sweat glands, which become functional at puberty, are phylogenetically much older than the eccrine glands, but in man this gland system has become rudimentary and distribution is largely confined to the axillae, breasts and urogenital areas. The apocrine glands are derived from the follicular epithelium and generally are associated with a hair although not all hair follicles possess them (1, 5, 6). Like eccrine glands they are coiled structures, but larger, 4.0 mm in diameter (1). Their secretion, which fluoresces, is a turbid fluid (pH 5.0-6.5) containing proteins, reducing sugars, ferric iron, and ammonia (5, 6). Response of sweat glands to external stimuli The sweating response provoked by sensory and emotional stimuli, and that elicited by thermal stimulation exhibit considerable variation (7, 8): maximal emotional sweating occurs on the palms and soles whilst maximal thermal sweating is seen on the fingers, arms, forehead and axillae (9). The eccrine glands of the axillae respond to emotional as well as to thermal stimuli. Below a certain 'critical' temperature (31-32øC) only microscopic amounts of sweat are visible on the skin. This 'insensible perspiration' results from periodic activity of groups of eccrine glands (10), and in a temperate climate is estimated to average about 4.2mg cm-2 h-1 (ll). Above this 'critical' level, a sudden increase in sweating occurs: this is termed 'reflex sweating' and with this type of response the output of a single eccrine gland on the arm or leg is between 0.222 and 0.258mg h-1 (12).

MEASUREMENT AND CONTROL OF PERSPIRATION 25 Apocrine glands respond to emotional and sensory stimuli only and, in comparison with eccrine secretion, the quantity of apocrine secretion is minute. Following stimulation a single axillary apocrine gland produces 0.001 ml fluid and then is unable to respond again for at least 24 h (5, 6). In the axilla the number of eccrine glands is four to five times that of apocrine glands (6) thus in this region eccrine secretion must obviously predominate. In man the presence of clothing limits the evaporation of sweat from the skin surface and, in the axillae in particular, the absorption of sweat by clothing can be uncomfortable, unsightly and frequently de- leterious to fabrics. This combination of factors has given rise to the cosmetic manufacturer's interest in the sweat glands, and his attempts to develop products which will diminish the production of sweat in the axillae. This in turn necessitates the use of techniques by which sweat gland activity can be observed and measured, so that the efficacy of possible anti- perspirant materials can be assessed. OBSERVATION AND MEASUREMENT OF SWEAT GLAND ACTIVITY AND ASSESSMENT OF ANTIPERSPIRANT EFFECT In vitro methods These methods of testing antiperspirant materials at best only give an indication of relative effectiveness and the systems used bear little or no resemblance to the human skin. The few methods that have been devised are based upon the fact that many antiperspirant materials, particularly aluminium salts, are astringent, i.e. they are capable of denaturing proteins. Protein precipitation Govette and Navarre (13) utilized protein precipitation from egg albumin as a rapid test for astringency. The amount of precipitation, assessed visually, was considered to be proportional to astringency and therefore to antiperspirant activity. Shrinkage and permeability o f frog skin The same authors used the degree of shrinkage of frog skin as a measure of astringency, whilst Ukrami and Christian (14) developed a test for anti- perspirants based upon the observation (15) that iodide and sodium ion