-10- 
The large end of the tip is drawn to a smaller diameter to form the 
point of the syringe. To do this heat a spot near the end in the small 
gas flame eind draw the ends to a diameter of somewhat less than 0*27 mms 
Sometimes two or three attempts must be made before a satisfactory product 
is obtained. The drawn section is then scj-atched with the sharp edge of 
a stone, broken off at the proper point, and groxmd back to an outside 
diameter of 0,27 mm* The outside edge is ground off lightly on the grind- 
ing wheel and the inside edge by spinning between thxmb and forefinger on 
the pointed stone under water, or with a drop of water covering the point. 
The point is then polished until it appears perfectly smooth when ma^iified 
about 60 times, by twirling the tip on the end of a soft piece of wood 
rubbed with jewelers* rouge, or by holding it against such a piece of wood 
moimted on the end of a moror shaft* The completed tip snould De 35 to 
50 nm« longa To attaoh it to the penoil, put it orer the plunger and draw 
it into the penoil until it sticks out about 25 an., then glue it into 
plaoe with an aoetone-soluble cement sush as is used to build model alr- 
plsnaes* This oement is easily dissolred when it beoones neoessax^ to 
replace the tip* 
The proper dlsoMters at the point of the glass tip are of utmost 
Importanoe* The outside diameter must be small enou^ to permit passage 
into the oriduot, and yet the inside diameter must be large enough to per- 
mit semen to be taken up easily axid quickly. The outside diameter should 
not be oyer 0*5 mm«, and 0*27 mm* is usually satisfactory. The inside dia- 
meter should not be less than 0.15 mm* These limits differ slightly from 
the dimensions recommended for the plastic syringe* 
When made as desoribed with 26-gage wire (0«41 mm.), the glass tip 
has a oapaoity of 1 mm*' for every 7*6 mm* of length* If a 27-gage 
(0*56 mm*) plunger is used, the oapaoity is 1 mm*^ for every 9*6 mm* of 
length* Gk>od instruments have been made with both sizes. Tips of smaller 
diameter are too delicate and have too small a capacity to be practical* 
Larger ones are more difficult to finish at the point with a large enough 
inside diameter and a small enough outside diameter* 
Plastio syringe. The plastic syringe is made of Lucite and brass* 
Most of itw parts must be made on a lathe* The Lucite tip is superior to 
glass because it is not easily broken, sharp edges are eliminated, and it 
can be machined and drawn to the desired diameter and bore. Threaded re- 
placeable tips can be readily changed and are easily cleaned. Lucite does 
not have the surface hardness of glass, and consequently will wear slowly. 
It softens when heated* (h*ease and oil can be removed with hexane, 
naphtha, methanol, or mild soap and water. 
The machining qualities of Lucite and brass are similar. Since this 
plastic is a poor conductor of heat, it is necessary to prevent overheating 
when drilling, cutting, or polishing. Drills should be lubricated with 
mineral oil or an oil solution C2 percent of soluble oil in water)* Fre- 
quent removal of chips is necessary when deep holes are drilled, and the 
holes are filled with the oil solution at each removal of the drill. 
Sharp drills and proper lubrication give uniform and polished inside walls 
to the tip, which result in good suction without a lubricant. 
