92 



THE AMERICAN MONTKLY 



[May, 



undertakes the study of minute mark- 

 ings. I have already referred to two 

 objects particularly, the scales of Po- 

 ditra and the siliceous frustules of P. 

 angulatum, not because the uncer- 

 tainties were any greater about these 

 objects than about others, but be- 

 cause they are familiar as test-ob- 

 jects ; and what has been said of 

 them is also true of all objects of the 

 same kind. Hence, the exact nature 

 of the markings of all diatoms and 

 insect-scales must be made out by 

 supplementing the ordinary micro- 

 scopical examination with experi- 

 ments of a different nature. 



To bring the bearing of the discus- 

 sion nearer to the field of work in 

 which some of the members of the 

 Academy are engaged, I would re- 

 mark that the nature of the so-called 

 " striped " or " striated," muscular 

 fibre cannot be positively determined 

 by direct examination with the micro- 

 scope. The " net-work " of the blood- 

 corpuscles, which was described be- 

 fore the Academy by Dr. Elsberg 

 some time ago, is shown to be, in all 

 probability, an optical illusion, and 

 the recent investigations of Klein and 

 Flemming on the structure of nuclei, 

 are without value, so far as any proof 

 of the existence of a minute net- 

 work is concerned. Dr. Ephraim 

 Cutter, of Boston, in the course of a 

 paper read before the Academy, de- 

 scribed some appearances in blood- 

 corpuscles, when examined with a 

 Tj^^-inch objective made by Mr. Tolles, 

 of Boston. I have never known any 

 more striking instances of misinter- 

 pretation than some that were em- 

 bodied in that paper, and while I 

 cannot admit that they were entirely 

 due to the imperfections of the ob- 

 jective, I am convinced that such 

 extraordinary powers as the -^- and 

 the -g^Q-inch are practically worthless. 

 Unquestionably, the results of the 

 thorough study which Professor Abbe 

 has undertaken will throw doubt 

 upon many observations of a nature 

 kindred to the above. 



The question will arise, to what 



extent can we rely upon the results 

 of microscopical work ? Practicall)', 

 I do not believe that many cases will 

 arise in which the microscopist will 

 be at a loss for a means of testing his 

 work and verifying his results. Thus, 

 the fractured frustule of a diatom may 

 reveal its structure, and the nature of 

 the markings upon the podura-scale 

 has been fully determined by the use 

 of electric current, which detached 

 the spines, and thus proved that they 

 were just what they appeared to be. 

 It is true that it is not always possi- 

 ble to do this ; hence, there will 

 always be some room for argument 

 and doubt. However, apart from 

 such comparatively few instances as 

 these, the evidence of the microscope 

 is reh'able. There can be no doubt 

 that every detail that is imaged diop- 

 trically is correctly pictured. It is 

 true that close lines or dots cannot 

 be resolved with the same assurance 

 of accuracy, but it must not be for- 

 gotten that the great end of micro- 

 scopical researches is not the resolu- 

 tion of close lines and dots. Indeed, 

 it is rarely that the microscopist who 

 works on other objects than diatoms, 

 insect-scales and test-plates, has oc- 

 casion to employ the utm.ost powers 

 of the instrument in such resolutions. 

 On the contrary, most of the work 

 done with the microscope, is of a 

 nature that requires excellent dioptri- 

 cal definition combined with sufficient 

 angular aperture to define minute 

 markings and isolated lines or par- 

 ticles, and there can be no question 

 raised about the eixistence of the 

 isolated particles or lines which are 

 portrayed. The flagella of certain 

 bacteria, which, if my memory serves 

 me right are not more than 1-200,000 

 of an inch in diameter, can be clearly 

 distinguished, and there can be no 

 question raised as to their existence. 



A Home-made Erector. 



I desire to call the attention 

 of those readers of the Journal 

 who are endeavoring to make every 



