Not until the Renaissance did our knowledge of hormones and sexuality start to progress, and Paracelsus (1493-1541) became the most important scientist of the age. Theophrastus Bombastus von Hohenheim (his real name) hailed from Switzerland, and his greatest achievement was to demonstrate that many diseases could be treated and that sufferers did not always need to endure passively. He introduced mercury treatment for syphilis, the aids of the sixteenth century.
In the eighteenth century the English surgeon John Hunter (17281793) did very important and original work, being the first to observe that the testes of animals slaughtered in the autumn were smaller than those slaughtered in spring. (The reason for this has only recently been discovered. The pineal gland at the base of the brain produces more melatonin when there is more sunlight, again boosting the production of hormones in the hypophysis, which in turn prompts the testicle to produce more testosterone and sperm.) Hunter also conducted experiments with animals. After transplanting a section of a cock’s testicle into a hen, he saw the hen assuming male characteristics, for example, acquiring a coxcomb. Unfortunately Hunter omitted to publish most of his findings, so that there are only sparse references to him in medical history books.
The German physiologist Berthold demonstrated in the midnineteenth century (1849) that when he reinserted the testicles of a castrated cockerel the creature once again developed a large comb and began behaving in a cockerel-like manner. Berthold, a professor at the University of Gottingen, wrote prolifically on every conceivable medical topic. What was his precise method? In an operation he removed the testicles of four cockerels, turning them into capons. Then he opened up the abdomen of two of the birds and implanted one testicle in each, so that that they were no longer attached to their previous nervous system. If they were to function, it would to be through the bloodstream. Berthold was incredibly lucky: antibiotics were still unknown and the capons could easily have succumbed to an inflammation of the abdominal membrane. But they survived, and the grafting of the testicles was successful. While those castrated birds in which no testicles had been replaced remained fat pacifists, the others turned back to cockerels in all respects. In his book on the male hormone Paul de Kruif puts it beautifully: ‘They crowed like the proud cocks they were, they fought till the feathers flew and they chased the females enthusiastically. Their beautiful bright-red combs and dewlaps went on growing.’ This was conclusive proof that the testicles fed a masculinizing substance into the blood.