66 



Prof. A. E. Wright. On the Measurement of [Aug. 5, 



n the first section of this paper, is fitted with a rubber teat ; sterile 

 oil is now aspirated into the pipette to replace the air in the capillary 

 stem and the lower part of the bulb. When this replacement has 

 been effected, the tip of the pipette is thrust down through the oil 

 contained in the thimble into the layer of serum, and this last is 

 aspirated into the pipette. When this has been accomplished, a little 



Fig. 5. Fig-. 6. 



of the covering oil is drawn into the capillary tube to seal the lower 

 orifice of the pipette. The serum, thus shut off from contact with the 

 air, is carried across into the first of the receiving tubes already 

 spoken of, and is driven out into this under cover of the oil. 



Another sterile testing pipette is now taken in hand, and the 

 procedure is repeated in all its details, the serum being carried across 

 from the first into a second receiving tube. 



Procedure Adopted for Measuring off Equal Volumes of the Serum and 

 Culture, and Mixing these without Contact with the Air. 



The next step is to mix the serum with the graduated dilutions of 

 the bacterial culture. These dilutions will have been prepared* by 

 diluting the culture with sterile broth, which has been previously 

 boiled up in order to remove the contained air. 



The procedure by which the serum and the culture are mixed is 

 essentially the same as the procedure employed for transferring the 

 serum from one vessel to another. The capillary pipette is first filled 

 in with a sufficiency of sterile oil, secondly with serum up to the mark 

 on the stem. Thirdly, a globule of oil is drawn in. 



Employing this globule of oil as a seal for preventing contact with 

 the air — it will presently function as an index globule — the pipette is 



* They may, if desired, be prepared under oil and from cultures anaerobically 

 grown under a covering layer of oil. 



