63 
The whole process does not take as long as the telling, and is much 
quicker and more accurate than the ordinary method of using the 
pipettes with a free hand. 
Method of using delivery gjipettes . — The method of using outflow” 
or ‘‘delivery” pipettes differs materially from that of using capacity 
pipettes. 
The rubber bulb is attached to the pipette as before, but in this 
case there is a T between the bulb and the pipette. From this T a 
small piece of rubber tubing, controlled b}^ a pinchcock, is located, as 
may be seen by reference to fig. 13. 
The pinchcock is kept closed while the pipette is filled to the proper 
graduation, which is accomplished just as in the case of the capacity 
pipettes described above. 
B}" opening the pinchcock the contents of the pipette, are allowed to 
flow out. When the last drop that will flow out of its own accord 
escapes, the proper time is allowed to elapse for drainage and the 
point of the pipette touched to the surface. By this procedure a 
very constant quantity of fluid remains in the capillary tip of the 
pipette. 
If the pipettes have been standardized to blow out this last drop, this 
may be done conveniently by closing the pinchcock and compressing 
the rubber bulb. 
The soft rubber ear syringes sold at any drug store make very good 
bulbs for this Avork. It is only necessary to cut off a small portion of 
the nozzle of the ear S3U*inge. The thicker- walled rubber bulbs made 
for Koch SAuInges respond more quickty and are more durable. The 
illustrations show the rubber bulbs attached directl}^ to the mouth- 
pieces of the pipettes. We liaA^e found it more con\^enient to bring the 
bull) b^" means of glass and rubber tubing to the base of the retort 
stand. 
I have used pipettes in accordance Avith these tAvo methods during 
the past tAveh^e months in work with toxines and antitoxins, and have 
concluded that they are quicker, more accurate, and more satisfactoiy 
than the old freehand technique. ® 
In working out the problems connected with the accurate methods 
of measuring giA^en A^olumes of toxine and antitoxin, I have had the 
help of the Bureau of Standards, and am indebted especially" to Dr. 
L. A. Fischer and Mr. S. Osborne, of the Bureau, for many useful 
suggestions. 
« This method was demonstrated at a meeting of the Society of American Bacte- 
riologists, Philadelphia, December 27, 1904. 
