Method of Preserving Marine Biological Specimens. 523 



and placed in dish No. 2 nnd washed, and then into No. 3 for a 

 final cleansing. A 3 X 1 glass slip is warmed, a small quantity of 

 " Deane's Medium " poured on to it, the frond of the alga arranged 

 in position therein, and a warmed cover-glass lowered carefully on 

 to it. The slide is then set aside for twenty-four or forty-eight hours, 

 when the superfluous medium can be cleaned off, three rings of Brown 

 cement or good gold-size applied, and when that is dry the slide is 

 finished off with a good black asphalte cement. I have slides prepared 

 in this simple manner some twelve or fourteen years ago which look 

 as fresh as they did on the first day that they were made. " Dean's 

 ]\Iedium " can be obtained through any of the vendors of micro- 

 scopical reagents, and is, I consider, a very useful mounting 

 medium for many botanical preparations, superior to the ordinary 

 glycerin jelly mountant, inasmuch that it permeates the tissues 

 more readily, does not alter their characteristic appearance or 

 shape, and air-bubbles are not so quickly formed. 



Formalin, properly used, is undoubtedly one of the most 

 valuable preserving fluids that the marine biologist can employ. 

 It can be diluted with sea-water just as well as with fresh, and 

 has such powerful antiseptic qualities that quite weak solutions 

 can be employed for preserving delicate structures ; it does not 

 generally produce any shrinkage of the tissues, and is a great time- 

 saver, as specimens can be placed at once into the solution it is 

 intended to store them in, instead of being passed through a series 

 of different grades of strength, as with alcohol. Unfortunately 

 formalin completely destroys certain kinds of calcareous structures, 

 such as the calcareous skeleton of some larval forms and the 

 spicules in calcareous sponges; therefore it should never be used 

 as a preservative for any larval or adult forms of the Echinodermata 

 or calcareous sponges. 



A good deal of confusion exists as regards the actual strength 

 of solutions, owing to the use of the terms "formaldehyde" and 

 " formalin " indiscriminately by many authors, and has been the 

 cause of failure and unsatisfactory results. Ten p.c. formalin and 

 10 p.c. formaldehyde are by no means one and the same thing, for 

 the latter is two and a-half times the stronger. Commercial 

 formalin as purchased contains a definite quantity of the gaseous 

 formaldehyde, which is generally stated on the manufacturer's 

 label either as formaldehyde 40 p.c. or formaldehyde 30 p.c. The 

 percentage of formaldehyde present should always be ascertained 

 at the time of purchase, and then it is a simple matter to make up 

 solutions of varying percentage. A 10 p.c. solution of formaldehyde 

 is made by adding 3(i0 c.cm. of water to 100 c.cm. of the stock 

 formaldehyde 40 p.c, and this will be found a very useful standard 

 solution to adopt. Personally I always have two standard solutions 

 ready to hand, namely the 10 p.c. and a 4 p.c, made up by adding 

 1 part formaldehyde 40 p.c. to 9 parts water. 



2 N 2 



