HCG is never found in the human body except during pregnancy and in those rare cases in which a residue of placental tissue continues to grow in the womb in what is known as a chorionic epithelioma. It is never found in the male. The human type of chorionic gonadotrophin is found only during the pregnancy of women and the great apes. It is produced in enormous quantities, so that during certain phases of her pregnancy a woman may excrete as much as one million International Units per day in her urine – enough to render a million infantile rats precociously mature. Other mammals make use of a different hormone, which can be extracted from their blood serum but not from their urine. Their placenta differs in this and other respects from that of man and the great apes. This animal chorionic gonadotrophin is much less rapidly broken down in the human body than HCG, and it is also less suitable for the treatment of obesity.
As often happens in medicine, much confusion has been caused by giving HCG its name before its true mode of action was understood. It has been explained that gonadotrophin literally means a sex-gland directed substance or hormone, and this is quite misleading. It dates from the early days when it was first found that HCG is able to render infantile sex glands mature, whereby it was entirely overlooked that it has no stimulating effect whatsoever on normally developed and normally functioning sex-glands. No amount of HCG is ever able to increase a normal sex function; it can only improve an abnormal one and in the young hasten the onset of puberty. However, this is no direct effect. HCG acts exclusively at a diencephalic level and there brings about a considerable increase in the functional capacity of all those centers which are working at maximum capacity.