Abstract: A syringe useful for taking samples of blood includes a barrel with a hollow needle at one end and a plunger positioned inside the barrel for regulating the amount of fluid inside the barrel. In order to control the volume inside the barrel which receives and contains the blood sample, a control element is associated with the plunger and the barrel to control the distance which the plunger can move in both inward and outward directions.

Abstract: An intravenous catheter assembly comprises a catheter with an elongate hollow tube and a hub connected to the tube and having an interior cavity communicating with the lumen of the tube. A needle is slidably positioned in the lumen so that its point protrudes slightly beyond the distal end of the tube, whereas the other end of the needle extends through the hub and sealingly contacts the same so that the hub is effectively closed. A blocking device is contained in the cavity which is adapted to block the entrance of the lumen after the needle is withdrawn from the catheter tube to prevent ready re-insertion of an instrument into the lumen; however, flow of fluids into the lumen is not blocked. The hub includes an access provision to the cavity whereby fluids may be deposited into the cavity for delivery to a patient after the needle has been withdrawn from the catheter tube.

Abstract: A catheter or like instrument having a variable flexural modulus for insertion into the body includes a length of flexible tubing having a normally relatively low flexural modulus. A first lumen inside the tubing provides a free flow path therethrough. Associated with the catheter tubing for controllably increasing its flexural modulus is a second lumen having a closed distal end and a proximal end adapted to be connected to a pressure source. An increase in pressure inside the second lumen serves to increase the flexural modulus of the catheter tubing to stiffen the same particularly during insertion of the tubing into the body. After insertion of the same, the pressure is controllable so that the catheter tubing is allowed to return to its normally low flexural modulus.