In order to investigate the effect of occlusion on the skin, the flexor sides of both upper arms were covered with column-shaped with column-shaped closed chambers, 30 mm in outer diameter, 20 mm in inner diameter, and 5 mm in height, which were made of polyethylene foam. The tops of the chambers were sealed by plastic films with various levels of water vapor permeability to control moisture in each chamber. The raised chamber walls prevented direct contact between the skin and the plastic film. After 24 h of application, morphological changes of the skin surface were observed microscopically by the nitrocellulose-replica method. Although no visual alterations were found on all areas of occluded skin, microscopic evaluation showed that simple occlusion by films induced an increase in the number of deepened skin furrows on the skin surface. this increase was associated with lower water vapor permeability of the films, as well as with higher values of both temperature and humidity of the test day. Thus, since conditions which facilitate perspiration from the skin tend to cause skin irritation, prolonged exposure of the skin to sweat by simple occlusion may act as a primary skin irritant.

The nuclear magnetic resonance method was used to investigate the state of water molecules in normal rat brain tissue in vitro. The transverse magnetization decay curve (TMDC) of the fresh brain tissue of adult rats (8- or 10-weeks-old) was biexponential, which could be interpreted in terms of two distinct transverse relaxation times (T2). Several factors that may affect the TMDC are discussed. It was concluded that the fast and slow components of T2 correspond to those of the water molecules of the intracellular and the extracellular spaces of normal rat brain tissue, respectively.

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