1893.] MICROSCOPICAL JOURNAL. 143 



num. P. decorum, etc., but perhaps the most interesting is a long, 

 narrow, and very delicate Plcurosig-ma which is new to the 

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

 straight. The living frustule appears entirely straight, the 

 front and side views having the same outline. This form enables 

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

 lively manner. The stria2 are so fine and delicate that an objec- 

 tive which resolves P, aiigulatum and P. elongatjim with ease 

 fails entirely with this. It is longer than P. intcrtnediuin of 

 Puget Sound. Its outline presents a more graceful curve and its 

 form is more delicate. 



The material also contains Syncdra from vS. superba down to 

 very minute kinds ; the elegant Schizonei)ia {Stazirofieis) crti- 

 ciger. with many others. Pacillaria paradoxa is in abundance 

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

 niatoplcura marina^ which appears like a Nitzschia^ many rare 

 Navicular Encyonema^ etc., are present, but the material requires 

 further examination in order to present a description of value. 



PROBLEMS. 



Note. — Topics are. suggested occasionally upon 'Mhich a variety of vtezvs 

 -Mould be desirable. The problems 'Mill be stated under this heading as 

 they arise, and persons having facts or opi9iions pertinent thereto are 

 invited to transmit the same, zvhich zvill be published under the heading, 

 " Letters to the Editor." 



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

 or best method of producing monochromatic illumination.? The 

 methods by sodium flame and ammonio-cupric solution seem to be 

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

 formulcE for the solution or manner of producing the sodium 

 flame in any 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. 



LETTERS TO THE EDITOR. 



Note. — This colu9nn is open to all correspondents -who write up07i the 

 topics enumerated under " Problems,"'' or -Mho give other i7ifortnation of 

 interest. The fact that a problem has been ajiswered once need 7tot deter our 

 friends from 7naking additional com77te7its. To facilitate refere7ice, corre- 

 sp07idents should cite the 7iu77iber as well as the page 07i which have ap- 

 peared letters a7id queries to zvhich refere7icc is 7nade. The editor is not 

 responsible for the views of others published in this periodical. 



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

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



