116 THE AMERICAN MONTHLY [May, 



carefully measure it in all directions and positions by aid of a 

 good eve-piece micrometer and make a drawing from the meas- 

 urements, which should be thoroughly verified by repeating them, 

 remembering that from their shape desmids usually present them- 

 selves in a more or less perspective and therefore unsymmetrical 

 view. On this account camera drawings and pictures of desmids 

 have not the value of a good drawing from careful measurement, 

 since it will be only by accident that the desmid will present it- 

 self symmetrically. The micrometer used bv the writer is a sys- 

 tem of silk fibres stretched across the opening in the diaphragm 

 of an eye-piece, in accordance with instructions in The Ameri- 

 can Monthly Microscopical Journal. It is almost continuously 

 in use. 



Having convinced yourself that your discovery is a new plant, 

 write its description in terms of botanical nomenclature (Wolle's 

 Desmids offers good examples), and publish in your local news- 

 paper, a copy of which with a copy of your drawing can be sent 

 to vour correspondents or to a scientific journal for publication. 

 The drawing mav be copied by photography or other methods. 

 A printed cop}' is best for ultimate publication, for written de- 

 scriptions are apt to be strangely translated. Do not be too sure 

 that your find is new. Alistakes are awkward, and while not al- 

 ways avoidable, detract from the value of one's work not only to 

 others but also to one's self. 



On Iinbeddiiig Animal Tissues in Paraffine f'oi* 8ectionizing. 



By Prof. H. L. OSBORN, 



HAMLINE, MINN. 



This method of preparing animal tissues for sectionizing is de- 

 scribed in all books of microscopical technique, and the descrip- 

 tion presented here merely repeats from them without adding any 

 specially new features. Since every detail in this connection is 

 important, I will risk being tedious and attempt to give an ac- 

 count by following which anyone can be sure of success. Every 

 step of the process must receive careful attention to insure success. 

 The work can conveniently be subdivided into several parts. 



I . Fixing or Hardening the Tissue. — One of the best modes 

 of hardening is by the picro-nitric acid method. Prepare the 

 hardening fiuid as follows : Dissolve picric acid crystals in distilled 

 water to saturation, add 2 per cent, of strong nitric acid ; a heavy 

 precipitate will fall ; filter and keep the filtrate for standard solu- 

 tion. Place in this standard solution, weakened with one-half or 

 two-thirds water, a piece of perfectly fresh tissue from a just killed 

 animal, or for small animals immerse the entire creature. Leave 

 it in from 3 to 6 hours. Then transfer it to 30 per cent, alcohol, 

 and in a few minutes thence to 50 per cent., and after an hour to 70 

 per cent. Keep it in 70 per cent., changing the alcohol daily till 



