1893.] MICROSCOPICAL JOURNAL. 143 



niitn, P. decorum, etc., hut perhaps the most interesting is a long, 

 narrow, and ver\ delicate Pleurosii^nia which is new to the 

 writer. It has the median line sligiitlv flexed, outline nearly 

 straii^ht. Tlie living frustule appears entirely straight, the 

 front and sitle views having the same outline. This form enahles 

 it to pierce through obstructions with ease. This it does in a 

 lively manner. The stria* are so Hue and delicate that an objec- 

 tive which resolves /'. angulatuni and /'. clongatum with ease 

 fails entirelv with this. It is longer than P. iutcrtncdium of 

 Puget Sound. Its outline presents a more graceful cur\e and its 

 form is more delicate. 



The material also contains Syticdra from vS\ superba down to 

 very minute kinds ; the elegant Sc/iizoncma {Stauroneis) crit- 

 ciger, with many others. Bacillaria paradoxa is in abundance 

 — another instance of its occurrence in deep saline water. Cy- 

 matoplciira marina, which appears like a Xitzschia. manv rare 

 Navicula. Encyoiictna, etc., are present, but the material requires 

 further e.xamination in order to present a description of value. 



PROBLEMS. 



Note. — Topics arc suggested occasionally upon ivJiich a z>ariety of vietus 

 xvould be desirable. The problems zvill be staled under this heading as 

 they arise, and persons haz'ing facts or opinions pertinent thereto are 

 invited to transmit the same, -vhich -vill be published under the heading, 

 ^^ Letters to the Editor." 



(9) Monochromatic Light. — What is the most convenient 

 or best method of producing monochromatic ilhnnination .^ The 

 methods b}- sodium flame and ammonio-cupric solution seem to be 

 capable of easy application, but I have been unable to Hnd 

 formulae for the solution or manner of producing the sodium 

 flame in anv of the ordinary works on the microscope. As many 

 eminent authorities hold that the next considerable advance in 

 microscopy must be through improvements in illumination by 

 monochromatic light, and as the performance of ordinary achro- 

 matic objectives is improved by its use. the subject becomes one 

 of importance. — F. P. 



LKTTKRS TO THE EDITOR. 



Note. — This column is open to all correspondents -vho write upon the 

 topics enumerated uttdcr " Problems,'''' or who giz'e other information of 

 interest. The fact that a problem has been answered once need not deter our 

 friends from ma king additional comments. To facilitate reference, corre- 

 spondents should cite the number as well as the page on which hai'e ap- 

 peared letters and queries to zvhich reference is made. The editor is not 

 responsible for the z'iews of others published in this periodical. 



(\z) Blood Stains. — In answer to the question of H. M. F., 

 relating to the preservation of blood-corpuscles (page 50, Fcbru-' 



