So what were Leaches Used for Back in the day in the Medical Field ?

Leeches are still used today. They were used to suck the blood of the sick person. Sickness was supposed to be caused by bad blood and it was thought that the person needed to lose some blood. A leech would be stuck on his body.

Today it is used in things like cauliflower ears. to remove blood clots, to bleed a patient because they thought that was the cure all doctors of old used to think that all sickness was due to a tainting of the blood. Poisoning of the blood. Leeches drew off the poison and "let" the person who was sick. The word "let" was used to describe the removal of blood through this process. well, they're not just for breakfast anymore

The leech has long been used in medicine, although today its use is mainly limited to limb reattachment procedures instead of the wide-ranging medical use of the past. The word leech either comes directly from or was influenced by the Old English word for "physician", l牵ce, which is related to Old High German l膩hhi and Old Irish liaig.

Leech saliva contains a number of compounds which assist in its feeding. An anaesthetic limits the sensations felt by the host (and thus reduces the chance of the host trying to detach the leech). A vasodilator causes the blood vessels near the leech to become dilated, and thus provide the leech with a better supply.

Lastly, the leech saliva contains a peptide called hirudin, which is a highly effective anticoagulant. The leech needs this to prevent blood clots (which would block its feeding) from forming in the wound created by its mouthparts. These properties are difficult to achieve using other medical techniques, and it is for this reason that leeches have come back into clinical practice in the last 25 years.