14 THE MICKOSCOPE. [January, 



QUESTIONS ANSWERED. 



Note. — Dr. S. G. Shanks, of Albany, N. Y., kindly consents to receive all sorts of ques- 

 tions relating to microscopy , whether asked by professionals or amateurs. Persons of all 

 grades of experience , from the beginner upward, are welcome to the benefits nf this depart- 

 ment. The questions are number ed for future reference. 



1 25. How are permanent mounts of spider 's web made ? — A. 

 R. 



Make a thick ring of varnish on a slip ; when dry, run a fresh 

 coat of varnish over it ; place the slide under a newly- made 

 (clean) web and press it upward so some of the lines of the 

 web will run across the varnish cell and be caught in the fresh 

 varnish ring ; set the slip aside, under cover, until the varnish is 

 dry ; add one or more coats of varnish to make a rather deep cell ; 

 cover as a dry mount. The web seems to relax somewhat and the 

 beaded or circular lines will touch the glass and adhere if the 

 cell is shallow. The beaded lines are best near the outer edge of 

 the web. The beads are glutinous and will adhere and flatten 

 against the glass weeks after the mount has been closed if the 

 cell is not deep enough. 



126. Is the poison in cheese and ice cream a ?nicroscopic 

 bacteria f — G. H, 23. 



This poison is probably the result of a slight putrefactive 

 change, which is always caused by bacteria. The poison has been 

 obtained as minute crystals, which will produce all the symptoms 

 of cholera morbus when swallowed. The poison is volatile at the 

 temperature of boiling water, and poisonous cheese may be 

 eaten with impunity after being cooked. These crystals are 

 called tyrotoxicon, meaning cheese poison, in Greek. See an 

 abstract in A?n. Mo. Mic. Jour?ial, vol. vi, page 175. 



127. Is there any sharp distinctio?z between fresh-water ana 

 ??iarine diato?ns ? — W. S. 23 . 



This query was sent to this department several months ago 

 and was referred to Prof. H. L. Smith, who has kindly furnished, 

 in substance, the following information : There is no sharp dis- 

 tinction between fresh-water and marine diatoms. There is but 

 one species of Pleurosigmcc, with diagonal stria}, occurring in 

 purely fresh water (and it is also brackish and marine) — P. 

 delicatulum. The Grammatophora do not occur in fresh water, 

 still there are closely allied genera which do. If one finds Nav. 

 virides or N. major, or Stauroneis phcenicent, or 6\ acuta, in 

 a fossil mass, he may be sure that it is a fresh-water deposit. 

 A Triceratium is good evidence of a marine deposit, " and yet 



