Alterations of intrascrotal temperature markedly affect spermatogenesis and sperm counts. In euspermic subjects, scrotal exposure for 30 minutes to a 150-watt electric light bulb resulted in reversal of the scrotal-rectal temperature ratio by a mean of 2.9 C. Such treatment on 14 consecutive days caused depression of spermatogenesis followed by rebounds to temporarily high sperm counts. Application of an ice bag to the scrotum for a mean of about 30 minutes cooled the testicular environment by a mean of 6.9 C. Such cold treatment on 14 consecutive days, beginning not less than 12 days following cessation of exposure to heat, stimulated spermatogenesis without initial inhibition, nearly trebling the mean pretreatment count. Oligospermic subjects responded to both heating and cooling faster and to a relatively greater degree, but less predictably, than did euspermics. The greatest increase in spermatogenesis followed sequential application of heat and cold, which suggested possible therapeusis in oligospermia.
Robinson D, Rock J, Menkin MF. Control of Human Spermatogenesis Intrascrotal Temperature. JAMA. 1968;204(4):290–297. doi:10.1001/jama.1968.03140170006002
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