^4 



THE AMEKICAN MONTHLY 



[April, 



EDITORIAL. 



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Vol in out of print. 



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Vol. V (1884). Nos. 2-12, gt.oo. 



Vol. VI (i8S5),;?i,oo. 



Mounting Media. — The several 

 articles that have heen published in 

 this journal (hnino^ the past year* 

 have drawn attention to this impor- 

 tant subject, and we hope to hear of 

 beneficial results from the application 

 of some of these media in special in- 

 vestigations. Their value is not fully 

 appreciated by most observers, but 

 when it is fully recognized some of 

 them will come into extensive use. 



There are some peculiarities which i 

 cannot escape notice when mounts in 

 the various media are compared. 

 For example, as Prof. Seaman has 

 observed, in the medium prepared 

 with anilin and sulphur there is a 

 brilliancy about the diatoms not ob- 

 served in the otlier media. Prob- 

 ably this is somehow related to the 

 dispersive as well as the refractive 

 power of the medium. The fact is 

 important, and deserves more atten- 

 tion than it has received. 



A medium of still higher refractive 

 index than any hitherto described has 

 been prepared by Dr. Morris, of New 

 South Wales. He has used sulphur 

 alone, which has a refractive index 

 • of 3, by melting it upon the slide and 

 pressing the cover with the diatoms 

 attached down upon it. A mixture 

 of selenium and sulphur, used in the 

 same manner, gives a medium with 



* Vol. vi (1885), pp. i5i, 182, 217 ; vii (1886), 3, 21. 



a refractive index of 2.3, and seleniuin 

 alone can be used, having an index of 

 2.6. The Amphipleura was shown 

 more than a year ago in sulphur by 

 Mr. G. D. Hirst, with a J water im- 

 mersion objective by Zeiss, ' in a man- 

 ner scarcely to be surpassed b}" the new 

 oil immersion, thus proving Dr. Mor- 

 ris' theory that a highly refracting 

 mounting medium enables lovv^-angled 

 objectives to compete in resolution 

 with the new oil immersions.'* It 

 seems scarcely necessaiy to point out 

 the error that this language might con- 

 vey. The mounting medium cannot 

 increase the limit of resolution of a 

 lens, since this is a function of the 

 angular aperture. What it does do 

 is to make certain objects, or the reso- 

 lution of fine details, more distinctly 

 visible when viewed with an objec- 

 tive capable of resolving them. Thus, 

 while mounting media do not add to 

 the resolving power, they nevertheless 

 may add very much to its effectiveness 

 as an instrument of research. This 

 is clearly seen in the case of minute 

 markings on diatoms, for, with Prof. 

 Smith's new media, the Aniphipleiira 

 is as easily resolved, with suital>le ob- 

 jectives, as the P1cu)-osig))ia aitgii- 

 latiim is with a good 4-inch. But, 

 apart from resolutions, the visibility 

 of any minute object is also greatly 

 increased by using the proper medium 

 for mounting, and the advantage of 

 the new media can be as well demon- 

 strated with an inch objective as with 

 a twentieth. 



Investigations of Microbes. — 

 It is a pity that persons in high places 

 do not more frequently consider the 

 evil consecjuences of undertaking in- 

 vestigations ^^■hich they are utterly 

 incompetent, either by training or 

 knowledge, to conduct. There seems 

 to be an opinion prevailing among 

 man}' that any one can make investi- 

 gations on microbes and their rela- 

 tions to disease ; so here and there a 

 professor in a college in some distant 

 educational centre suddenly • springs 



* Free. Roy. Soc. N. S. W. (1884). 



