196 



SCIENCE. 



[N. S. Vol. XIX. No. 474. 



accommodated as promptly as possible. The 

 limited number of plates available will of 

 course cause more or less delay in complying 

 with many requests. A prompt return of each 

 plate is to the interest of all. A self-addressed 

 envelope with four cents in postage affixed 

 should accompany each application. 



Failure to observe the phenomenon can only 

 result from an insufficient resting of the eyes. 

 Half an hour in subdued light such as lamp- 

 light, followed by four or five minutes in 

 absolute darkness is the sine qua non of s\ic- 

 cess. 



The magnifying glass employed should have 

 a power of five or six diameters. A Codding- 

 ton lens, or Hastings triplet is suitable. 



E. W. Wood. 



Johns Hopkins University. 



SPECIAL ARTICLES. 



THE OCCURRENCE OF ZINC IN CERTAIN 



INVERTEBRATES. 



In the course of an investigation on the 

 chemical physiology of certain invertebrates, 

 undertaken under the direction of Dr. La- 

 fayette B. Mendel, it was found that the ash 

 of the hepato-pancreas of the large carnivorous 

 gastropod, Sycotypus canaliculatus, contained 

 an element hitherto unobserved in such con- 

 nection, namely zinc. So far as the writer 

 is aware, this element has never been observed 

 as a normal constituent of the tissues of 

 any animal, vertebrate or invertebrate. The 

 reaction by which zinc was first suspected was 

 the ordinary ferrocyanide test for ferric iron 

 in acid solutions. Not only was iron present, 

 as indicated by the blue color, but some other 

 metallic element as well, giving a marked 

 slimy precipitate. Further investigation 

 showed the presence of a heavy metal having 

 all the characteristic chemical properties of 

 zinc. 



Quantitative separations were made difficult 

 by the presence of very large amounts of 

 phosphoric acid, and the basic-acetate method 

 was resorted to. The well-known limitations 

 of the latter malie it, however, scarcely more 

 than of qualitative value. By this method 

 samples of ash from Sycotypus canaliculatus 



gave approximately eleven per cent, and 

 twelve per cent, respectively of ZnO. 



Further separations have since been made 

 by means of Hampe's well-known method 

 (slightly modified),* depending upon the pre- 

 cipitation of ZnS from a formic acid solution 

 of sufficient strength to prevent the precipita- 

 tion of the iron. By this method concordant 

 results have been obtained as shown in the 

 table below. At the same time qualitative 

 examinations were made of specimens dredged 

 from various parts of Long Island Sound 

 about New Haven, and in all cases zinc was 

 found in large quantities in the ash of 

 Sycotypus and Fulgur carica. 



Copper was estimated electrolytically in 

 each case; in one sample by the rotating 

 cathode method of Gooch and Medway. Iron 

 was determined by permanganate titration in 

 the usual way. Blanks were run through to 

 detect the possible presence of zinc in the 

 reagents, and great care was exercised through- 

 out to prevent any contamination. 



Other tissues besides the hepato-pancreas 

 were incinerated and examined, and other 

 gastropods and Crustacea dredged from the 

 same localities were also tested. With the 

 exception of the blood of Sycotypus^ no fur- 

 ther occurrence of zinc has yet been detected. 



The following table of ash analyses summar- 

 izes the result of the investigation as far as 

 it has been carried. 



Si/coti/pus 



paucreas. 

 Sf/coti/pus, 

 Si/L-oft/pus. 

 A'l/coltjpn 

 Sjicofypv 

 St/cohjptf 

 Sjlvotfipu 

 Blood of Sycotiipi 

 Fulgur. 

 Fulgur. 

 Fulgur. 



, 1903 

 1903 

 1903 

 , 1903 

 ,1903 

 , 1903 

 , 1903 

 , 1903 

 1903 

 , 1903 

 , 1903 



0.84* 



0.84SS 



Present 



7.83^ 

 Present 



Present 

 11.97!S 

 10.81^ 

 19.005« 

 23.38* 

 18.80* 

 18.60* 



Present 



The following other marine forms have 

 been examined for zinc, with negative or doubt- 

 ful results in all cases : Urosalpinx cinerea, 

 Mytilus edulisj Modiola plicatula, Argina 



* W. Hampe, Chemiker Zeitwig, IX., 543 (esti- 

 mation of zinc ) . 



