November 17, 1905.] 



SCIENCE. 



637 



On the Effect of Magnesium Salts upon the 

 Excitahility and Conductivity of Nerves. 

 S. J. Meltzer and John Auer. 

 Numerous applications of solutions of mag- 

 nesium salts to the sciatic, pneumogastric, 

 depressor and sympathetic nerves of rabbits 

 failed to produce any evidence of excitation, 

 but in each case there resulted sooner or later 

 a profound inhibitory effect upon the conduct- 

 ivity of the nerve under observation. Thus, 

 after application to the sciatic nerve, the con- 

 duction of motor and sensory impulses was 

 manifestly inhibited.: a strong stimtdus ap- 

 plied belovp the ' block ' caused strong contrac- 

 tions of the muscles of the thigh but no pain; 

 vphen applied above the ' block,' stimulation 

 induced pain but failed to cause contraction. 

 Such effects vpere obtained v^ith hypertonic as 

 well as with isotonic and even with strongly 

 hypotonic solutions. The weaker the solution 

 the longer it took to establish complete inter- 

 ruption of conductivity. Conductivity could 

 be restored by washing the nerve with Ringer's 

 solution. William J. Gies, 



Secretary. 



DISCUSSION AND CORRESPONDENCE. 



THE GEOGRAPHICAL DISTRIBUTION OP STUDENTS. 



To THE Editor of Science : In Dr. Tombo's 

 interesting article on ' The Geographical Dis- 

 tribution of the Student Body at a Number 

 of American Universities ' which appeared in 

 Science for October 6, 1905, he was careful to 

 state that ' in the case of Harvard University 

 the students of Eadcliffe College (undergrad- 

 uate women) are not included.' May I amend 

 that statement by saying that only men were 

 counted in the Harvard table, the graduate 

 students as well as the undergraduate students 

 of Radcliffe College having been excluded. 

 Had these 407 students been included, several 

 comparative statements in the article would 

 have been affected. Harvard would have led 

 in the North Atlantic division by 47, and 

 would have gone from fourth place to third 

 place in the South Atlantic division. In the 

 line of grand totals Harvard would have led 

 by 361, Columbia being second and Michigan 

 third. Had women been wholly omitted or 



separately counted in Dr. Tombo's table, sev- 

 eral rearrangements would obviously have been 

 necessary. 



Jerome D. Greene. 

 Harvard University. 



THE making of LANTERN SLIDES. 



To the Editor of Science : Every one knows 

 how troublesome it is, in the making of lan- 

 tern slides from a variety of objects, to accu- 

 rately center the images on the negative 

 plates; how very troublesome it is to get a 

 centered lantern slide from an eccentric nega- 

 tive, and how much time is required in cutting 

 paper mats for bounding the field of a lantern 

 slide. For several years I have employed a 

 method which I find obviates these difficulties 

 almost completely. 



In making my negatives I take pains to get 

 the desired size of image, but do not take the 

 trouble to center the image upon the spot 

 where the negative plate is expected (?) to be. 



I take these negatives and trim them by 

 means of a cutting diamond to the size of the 

 transparent square desired on the lantern 

 slide. I can trim thirty negatives in fifteen 

 minutes. 



I then take my lantern plates, lay them 

 film side up on a black ground, lay a trimmed 

 negative centrally on each, and print by a 

 light held above. 



The resulting positives are perfectly cen- 

 tered, and the desired field is sharply bounded 

 by a nearly opaque border which is as satis- 

 factory as a carefully cut paper mat. 



W. S. Eranklin. 



SPECIAL ARTICLES. 

 orthogenetic variation. 



Since I am responsible for the term ' ortho- 

 genetic variation,' whilst the far greater idea 

 of ' orthogeny ' falls to the credit of the late 

 Theodor Eimer, I am anxious that it should 

 not be misrepresented. 



The paper by Mr. Robert E. Coker, entitled 

 ' Gadow's Hypothesis of Orthogenetic Varia- 

 tion in Chelonia,' Johns Hopkins University 

 Circular No. 178, May, 1905, calls for some 

 remarks on my part by way of protest and 



