Dialysing fluid, also known as dialysate, is a solution used in the process of dialysis to remove waste products and excess fluids from the blood. There are a few key differences between dialysing fluid and normal body fluids:

1. Composition: Dialysing fluid is specially formulated to contain specific concentrations of electrolytes, such as sodium, potassium, calcium, and bicarbonate, to help maintain the balance of these substances in the body during dialysis. The composition of dialysing fluid is carefully controlled to mimic the electrolyte levels in normal blood.

2. Osmolarity: Dialysing fluid has a specific osmolarity, which refers to the concentration of solutes in a solution. The osmolarity of dialysing fluid is adjusted to promote the movement of waste products and excess fluids across the dialysis membrane while preventing the loss of essential substances from the blood.

3. pH Level: The pH level of dialysing fluid is adjusted to ensure it is within the normal physiological range. This helps maintain the acid-base balance in the body during dialysis.

4. Sterility: Dialysing fluid must be sterile to prevent infection. It is typically packaged in pre-sterilized bags or containers.

Overall, the main difference between dialysing fluid and normal body fluids is the controlled composition and osmolarity of the former, which is specifically designed for the purpose of dialysis.