248 



SUMMAKY OF CURRENT RKSEARCHES RELATING TO 



in every case to subject a sample of water to a second centrifuging at 

 as high a speed as available. 



The best method of removing the centrifuged organisms from either 

 the large or small tubes is to pipette off all the water except a very small 

 drop at the bottom, and then to suck up this remaining drop and 

 forcibly expel it several times. In the case of the small tubes these 

 operations are most easily performed with a RoQsselet " thistle-head " 

 pipette drawn out to a very fine point. A portion of the drop of water, 

 or the whole of it if very small, is then transferred to a glass sKp, live- 

 box, or compressor. At this stage a further concentration of the 

 organisms can easily be carried out if necessary by taking a drop of 

 water two or three times larger than that actually required and allowing 



Fig. 39. — Plan and elevation of "haematocrit " head adapted to carry small 

 Ivase-shaped tubes holding about 1^ c.cm. Two-thirds actual size. 



it to evaporate to the desired size. In any case it is advisable to allow 

 the drop to stand a few minutes before spreading it out with the cover- 

 glass, as some at least of the organisms settle to the bottom and so do 

 not escape so easily to the margins when pressure is applied to the 

 cover-glass. 



The principal use of the centrifuge in pond-life work, as in marine 

 plankton work, is not to take the place of other methods of collection 

 such as nets and filters, but to be accessory to them. As such an acces- 

 sory piece of apparatus the centrifuge has evidently come to stay, and 

 no method of collection depending entirely upon straining or filtering 

 processes can be considered sufficient in the future. 



New Medium for Cultivating Bacillus diphtherise.* — T. T. 

 Rankin describes a medium for cultivating Bacillus diphtherise, by 

 which the bacteria can be recognized without the aid of the Microscope. 

 It consists of 8 parts sheep's-blood serum, 1 part bouillon, • 5 p.c. glu- 



* Journ. Hygiene, ii. (1911) p. 291. 

 a911) p. 760. 



See also Centralbl. Bakt., I'e Abt. Ref., 1. 



