202 An Apparatus for Liquid Measurement by Drops. 



tube, may be fitted on by a ferrule of washed rubber tubing or of good 

 cork. A dropping-point to give watery drops of \ e.c. way be formed of 

 tubing 14£ mm. external diameter. The dropper is held in a stand at a 

 height convenient to allow a rack of test-tubes to be slid under the dropping- 

 point. 



The drop-rate may be regulated as desired by fitting inside the dropping- 

 tube, and within forceps-reach of the orifice, a 

 throttle made of suitably drawn out capillary tube. 



The author has found the apparatus efficient in 

 the following applications : — 



(1) Comparison of surface-tension of liquids, in 

 quantity as little as \ c.c, e.g. in testing the value of 

 the meiostagmin reaction in syphilis. 



(2) As the drop yielded by one pipette differs by 

 not more than a fraction of 1 per cent, from the 

 drop similarly yielded by another pipette similarly 

 gauged in the same hole, the method may be used, 

 with successive fresh pipettes, for rapidly and 

 accurately measuring off small quantities of any 

 liquid, from 025 c.c. to, say, 0"004 c.c. of watery 

 liquids of high surface tension, or even smaller 

 quantities of liquids of low surface tension, for 

 instance, in : — 



(a) Measurements of various small quantities, in 

 e.g. Wassermann reaction, micro- Wassermann re- 

 action, and other complement-fixation tests ; Widal 

 reaction ; alkalimetry, acidimetry, and other volu- 

 Fig. 2. metric tests; testing cultures and disinfectants ; and 



in pharmacy. 



(b) Direct estimation of cells, numerically, and roughly qualitatively, in 

 small drops of cerebro-spinal fluid, dried on a slide. 



(c) Blood-count, red cells and white cells, from drops of diluted blood, 

 similarly dried. 



(d) Direct counting of bacteria in small dried drops of diluted vaccines, 

 distilled water, domestic water, sewage effluent, diluted milk. 



(b), (c), and (d) yield permanent preparations. 



