NOTES AKD MEMORANDA. 



On Certain Methods of Cutting and Mounting Microscopical 

 Sections.— It is many years since Leiickart; first suggested 

 the cutting of thin slices of an animal and mounting them 

 as transparent objects. Now it is possible to cut a worm 

 into sections from end to end and be sure that every section 

 is perfect, or to obtain a series of iifty sections from the 

 morula of a Medusa but one hundredth of an inch in 

 diameter. 



The methods I am about to describe are modifications of 

 older processes and constitute the latest stage of develop- 

 ment of the section-cutter^s art. 



Hardening . — Any of the ordinary hardening methods may 

 be used, but it is essential that all trace of acid should be 

 removed in order to obtain good staining results. Corrosive 

 sublimate is an exceedingly useful hardening reagent, and 

 tissue treated with it stains as readily as if treated with 

 alcohol only. The solution used is a concentrated one, the 

 fresh tissue or living animal is placed in it, for 15 to 30 

 minutes according to its size, it is then washed in water 

 and transferred to alcohol of 50 per cent. : a large relative 

 bulk of this must be used and the tissue well permeated by 

 it, otherwise some corrosive sublimate is left in the tissue 

 and is throvt'n down in needles when strong alcohol is 

 added. ^ After 24 hours the tissue is transferred to alcohol 

 of 70 per cent., and after 24 hours to alcohol of 90 per cent, 

 and then to absolute alcohol. With large pieces of dense 

 tissue this should be changed once or twice. After two or 

 three days the tissue is ready for staining. If time is an 

 object and no acid has been used in the hardening, the 

 tissue may be transferred directly from alcohol of 70 per 



' We owe this, and mauy other excelleat histological methods, to Dr. 

 Arnold Lang, of the Zoological Station at Naples. 



