ABSTRACT
The sucking pump of Rhodnius drives blood from the host into the abdomen at a rate of up to 20 mm.3/min. The stylet canal is 8–10 μ diameter at the apex and the rate of taper is not more than 1 μ increase in diameter/100 μ length.
The pressure required to force water through such a tube at that rate is about 2 atmospheres. The pressure required with blood would be higher.
The musculature of the pump is theoretically capable of exerting a force on the pump piston of at least 2·5 atmospheres, while contracting at the required speed.
The bug is capable of feeding at near to the normal rate when the surrounding pressure is 0·2 atmospheres and also against a pressure gradient of 0·2 atmospheres.
The retreating contact angle of insect cuticle to a blood-air interface is very low.
It is suggested that the high tensile strength of the blood and the low contact angle of the pump walls to the blood are the reasons why cavitation does not occur in the feeding pump of Rhodnius when the internal pressure drops below the vapour pressure of blood.
