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TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



plate is engraved with fine lines cnt in by means of a 

 diamond, and each plate has a definite linear system. 

 When the glass plate is in focns two parallel lines, in a 

 direction perpendicular to the observer, are seen. When 

 the side screw is turned successive lines are brought into 

 the field of view. The rotation of the other screw 

 gradually brings into view the whole of the space between 



Fig. 7 



two given lines. The whole glass plate can thus, starting 

 from one corner, be gradually brought into the field of 

 view, and no part of it can possibly be overlooked. When 

 a known volume of the diluted fluid is brought on to the 

 glass plate the number of individual organisms of a given 

 species can be readily determined, but the dilution is best 



