Any undesirable substance or group of cells that has made its way into part of the body.
To cause to penetrate in this way.
To invade or penetrate a tissue or organ.
To surreptitiously penetrate, enter or gain access to.
To send (soldiers, spies, etc.) through gaps in the enemy line.
To pass through something by filtration.
To move from a vein, remaining in the body.
To cause (a liquid) to pass through something by filtration.