492 



SCIENCE. 



[N. S. Vol. XI. No. 274. 



Where the ink has been is now less active 

 than the rest of the plate. Here are slides 

 which show these positive and negative 

 pictures. Another way of modifying the 

 zinc surface is interesting. You have seen 

 that the ordinary zinc surface which has 

 been exposed to air and moisture is quite 

 inactive, but if a bright piece of zinc be 

 immersed in water for about twelve hours, 

 the surface is acted on ; oxide of zinc is 

 formed, showing generally a curious pat- 

 tern. ISTow if the plate be dried, it will be 

 found that this oxide is strongly active, and 

 gives a good picture of the markings on the 

 zinc. The oxide evidently holds, feebly 

 combined or entangled in it, a considerable 

 quantity of the hydrogen peroxide, and it 

 requires long drying or heating to a higher 

 temperature to get rid of it. Also, if a zinc 

 plate be attacked by the hydrogen peroxide, 

 the attacked parts become more active than 

 the bright metal. Thus place a stencil on a 

 piece of bright zinc, and expose the plate 

 to the action of an active plaster of Paris 

 slab, or to active blotting-paper for a short 

 time, then, on removing the stencil, the 

 zinc plate will give a very good picture of 

 the stencil. Any inactive body — for in- 

 stance, a piece of Bristol board or any or- 

 dinary soft paper — can be made active by 

 exposing it above a solution of peroxide, or, 

 more slowly, by exposing it to a bright zinc 

 surface. If, for instance, a copper stencil 

 be laid on a piece of Bristol board, and a 

 slab of active plaster of Paris be placed on 

 the stencil for a short time, the Bristol 

 board will even, after it has been removed 

 from the stencil for some time, give a good 

 picture of the stencil. Drying oil and other 

 organic bodies may be used in the same way 

 to change the paper. A curious case of this 

 occurred in printing a colored advertise- 

 ment cut out of a magazine, for there ap- 

 peared printing in the picture which was 

 not in the original. This printing was ulti- 

 mately traced to an advertisement on the 



opposite page, which had been in contact 

 with the one which was used ; thus this 

 ghostly effect was produced. 



I believe, then, that it is this active body, 

 hydrogen peroxide, which enables us to 

 produce pictures on a photographic plate in 

 the dark. There are many other curious 

 and interesting eiiects which it can produce, 

 and which I should like to have shown you, 

 had time permitted. 



I would only add that this investigation 

 has been carried on in the Davy Faraday 

 Laboratory of this Institution. 



William James Russell. 



DEGENERATION IN THE EYES OF THE COLD- 

 BLOODED VERTEBRATES OF THE NORTH 



AMERICAN CA VES.* 

 " Degeneration, " says Lankester, " may 

 be defined as the gradual change of the 

 structure in which the organism becomes 

 adapted to less varied and less complex 

 conditions of life ; whilst elaboration is a 

 gradual change of structure in which the 

 organism becomes adapted to more and 

 more varied and complex conditions of 

 existence." 



Degeneration may affect the organism as 

 a whole or some one part. I propose to 

 speak not on degeneration in general but to 

 give a concrete example of the degeneration 

 of the parts of one organ. 



The eyes of the blind vertebrates of 

 North America lend themselves to this 

 study admirably because different ones have 

 reached different stages in the process, so by 

 studying them all we get a series of steps 

 through which the most degenerate has 

 passed. This enables us to reach conclusions 



* Presidential address at the meeting of the Indiana 

 Academy of Sciences, Dec. 27, 1899. The detailed 

 account of the eyes, whose general features are given 

 here, has in part been published in Roux's Archiv f. 

 Entwickelungsmechanik, VIII., and will in part be 

 published in the Proceedings Am. Microscopical So- 

 ciety for 1899. 



