This is the removal of fluid from the body by means of suction. It is used to determine the presence and character of fluid, as well as to remove it.

There are several types of apparatus generally spoken of as aspirators, the best known of which is Potain's. It consists essentially of a glass reservoir from which the air is exhausted by means of a small pump, and a fine hollow needle connected with the reservoir by means of rubber tubing. Stop-cocks control the passage both from needle to reservoir and from pump to reservoir.

To use the apparatus the air should be first exhausted from the reservoir by means of the air pump, and its con nection with the air pump then closed by the stop-cock. The needle should then be inserted and the cock opened which controls its connection with the reservoir. Under these conditions, if the needle is in contact with fluid, the negative pressure of the vacuum will draw the liquid through the tubing into the receptacle. As long as there is fluid it will continue to flow unless the needle becomes plugged with some debris, or the receptacle gets nearly full. In the former case it will be necessary to withdraw the needle, and by reversing the air pump, force the obstructing matter out of the needle or pipe. In the latter case disconnect the needle tube, after compressing it, and then empty the receptacle, which is usually a bottle, then re-exhaust the air and proceed as before.

In using an aspirator the same rules of precaution should be observed as are taught with reference to the trocar. The aspirator has the advantage of a very fine needle whereby the wound, if such it can be called, is very minute; the needle causes little pain in its introduction and it is so small that there is almost no danger from trauma; the suction permits of the removal of fluid, which lack of pressure might fail to expel with other instruments. Almost every organ of the body has been punctured by the aspirator without untoward results. For the removal of pleuritic effusions it is unquestionably the first choice, in which case puncture may be made into the eighth or ninth intercostal space about two inches below the angle of the scapula, or between the seventh and eighth ribs in the post axillary line. Insert the needle close to the upper border of the lower rib to avoid wounding the intercostal artery.

In aspirating for pericarditis with effusion the puncture is usually made in the fourth intercostal space one inch from the left border of the sternum, the needle being pointed upward and toward the median line. It may also be made in the fifth intercostal space one and one-half inches to the left of the sternum.

In aspirating a joint where there is no sepsis, and recognizing the danger of carrying infection through the skin by the needle, and the difficulty of cleaning the skin, it is a wise procedure to make a slight incision through the skin with the scalpel, and into this tiny opening so made, pass the needle on to the joint.

In introducing the needle it should be grasped firmly and thrust quickly through the skin, then pushed on more slowly until the fluid is reached. When withdrawn the puncture should be sealed with a bit of cotton and collodion or adhesive plaster.