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THE USE OF THE CENTRIFUGE IN POND-LIFE WORK. 



By D. J. ScouRFiELD, F.Z.S., F.R.M.S. 



{Bead April 2otJt, 1911.) 



As is very well known, the centrifuge in various forms has long 

 been used in medical work for the sedimentation of certain 

 constituents of blood, urine, milk, etc. It is also pretty generally 

 known that more recently it has been extensively used in 

 bacteriological work and in that vigorous young branch of 

 zoology, experimental embryology. Its use in connection with 

 the investigation of the more minute organisms occurring in the 

 sea and in fresh waters, although not actually novel, is not so 

 well known, and a few remarks on this subject, especially in 

 relation to pond-life work, may therefore be of value. 



The application of the centrifuge to the collection of minute 

 organisms in water was apparently first suggested by Cori (2) 

 in 1895. Very soon after, Dolley (4) constructed a special 

 kind of centrifuge, wliich he called a Planktonokrit, for the same 

 purpose, and almost simultaneously Kofoid (6) and Field (5) were 

 also experimenting in a similar direction. 



During the next ten years or more, however, the method was 

 not at all widely adopted, probably because it was looked upon 

 merely as an alternative to the more usual and in many respects 

 more simple and convenient methods of concentration by means 

 of fine gauze nets, filter papers and settling tubes. It was 

 not, in fact, until Lohmann (7) in 1908 published his splendid 

 paper on the determination of the absolute quantity of plankton 

 in sea water that it was realised that the centrifuije was 

 indispensable so far as the minutest forms of plankton were 

 concerned, and that it was therefore not to be regarded as a 

 substitute for the other methods of collection, but rather that it 

 had its own proper place side by side with them. The necessity 

 for the employment of some more effective means than any of 

 those hitherto in use for collecting the smallest organisms was 

 suggested to Lohmann by his observations on the Appendicularia. 

 He found that these creatures, owing to the exquisitely fine filter- 

 ing apparatus with which they are provided, were able to secure 

 enormous numbers of very small protists in water which yiplded 

 but slight evidence of the existence of such forms wJien tested in the 



JouRN. Q. M. C, Series II. No. 69. 17 



