sorption rates and absorption patterns when one compares or scales across species and frequencies. In the interest of extrapolating animal teratologic studies to man, we can attempt to scale to a limited degree. For example, let's look at the teratologic effects of 2450 MHz in the mouse and rat. The mouse fetus responds to daily exposure at 2450 MHz and 28 mW/cm2, conditions very related to SPS, with a body weight decrease. The rat fetus appears unmoved under these conditions. If we factor into this exposure situation the scaling for relative absorption rates, we see that the rat had absorbed only about 1/5 that which the mouse had absorbed. One might suggest an experiment where the power density is increased 5 times to 150 mW/cm2 as compensation for the lack of absorption in the rat, and so that the rat fetus might respond like the mouse fetus does. But, the rat dam does not survive such power densities. Death due to over-exposure at 2450 MHz begins to occur in the rat at only 40 mW/cm2. When the distribution of energy in mouse and rat is compared, the patterns of energy distribution may account for both the lack of rat fetal changes and death of the rat dam. The energy distribution is surface-directed in the rat. At 28 mW/cm2, the fetus has little chance to receive a significant portion of this energy as it is buried deep in the dam's tissues. At higher power densities, the surface circulation of the dam, normally used for heat loss, brings into the body the energy which cannot be disposed of otherwise; death ensures before the fetus can be altered. Now, the rat may not be a good model for understanding teratologic mechanisms at 2450 MHz, while the mouse is. But, scaling of energy distribution and relative absorption rates from rat to women may represent a reasonably good model. In both these species, energy distribution is surface-directed and there is little chance for the energy to reach the fetus directly. And the relative absorption rates at 2450 MHz can be expected to be low in women. Women in a 2450 MHz field may experience only 1/10 of the rat's or 1/50 of the mouse's absorption rates. There are many other factors which have been ignored in the conclusion that the rat might be a model for pregnant women exposed to an SPS-type situation on the ground (Figure 3). One of these factors is the metabolic tolerance of man. Because of a much greater capacity to rid the body of excess heat by the use of mechanisms like sweating, man's tolerance to heat is 3-5 times greater than that of the rat. This means that surface directed distributions of energy, as is the case for 2450 MHz in both man and rat, have a much more important consequence in the rat. Non-uniform absorption which is mostly distributed on the body surface, as is the case with women in a 2450 MHz field, may not represent a hazard to the human fetus, even if power densities do reach 23 mW/cm2. Reproductive aspects for men in such situations is possibly a different case. The factors we have used for extrapolating animal fetal effects to human fetuses can also be brought into play in extrapolating testicular effects in animals to men. As the human fetus is protected by distance from surface-directed absorption, testes tissue is not so protected. The testes lie immediately below the skin surface, and a significant fraction of the energy can be expected to deposit directly in the tissue of the testes. The testes tissue is unique in that its capacity to function is related to its temperature. Structural and physiologic mechanisms are normally used to help prevent testicular temperatures from reaching body temperatures, because it is at body temperature that sperm production is restrained or ceases. Unless actual
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