[3] PRESEEVATION OF MICROSCOPIC MATERIALS. 609 



distinct specimen or distinct series sbould be wrapped separately and 

 have a label securely attached, giving tlie date of collection, localitj', 

 «S:c. In the case of embryos, care should be taken to record the age of 

 the ditierent series where this is known, and in the cases of tishes, am- 

 phibians, and some articulates, this nmj be known very exactly. To 

 prepare a series of embryos of fishes, for example, and especially where 

 their eggs are artificially hatched in some kind of hatching apparatus, 

 it is very easy to prepare a series of specimens at intervals of, say, every 

 twelve to twenty-four hours, and to place the separate lots of different 

 ages in different vials, so that the investigator may use the material so 

 prepared in a very complete study of the development of the form. In 

 the preparation of such series it is important to give the date, and, if 

 possible, the hour of the day when the eggs were impregnated, and to 

 indicate upon a label within or pasted on the outside of the bottle, the 

 exact age of the contents. The locality and collector's name should also 

 be given. Labels placed within the vials so as to be immersed in the 

 preservative agent should not be written in ordinary ink, but with a 

 soft lead-pencil, as common writing ink is liable to become effaced from 

 the paper by the solvent action of the preservative fluid. India ink, 

 according to Semper, when dissolved in strong acetic acid, makes a 

 black marking fluid which will remain perfectly black and legible in 



alcohol for years. 



PRESERVATIVE AGENTS. 



All of the best preservative agents tend to harden animal tissues. 



Alcohol. — When alcohol of 95 per cent, is used it should almost 

 always be diluted. One of the few cases in which 95 per cent, or 

 absolute alcohol may be used to advantage is in the preservation of 

 sponges, as I am informed by Dr. Beuj. Sharp. These may be im- 

 mersed in the very strongest alcohol as soon as they are removed from 

 the water, a recent investigator having found that for the study of their 

 minute structure this was the best preservative medium, after the un- 

 satistactory trial of a great many. The collared flagellate cells lining 

 the respiratory and digestive cavities of these organisms are thus best 

 preserved. 



In almost all cases, however, the use of very strong alcohol is fol- 

 lowed by more or less extensive and injurious shrinkage of the object, 

 especially if it is very soft and watery, as in the cases of embryos, 

 polyps, and mollusks, more particularly. In these cases the mixture 

 first used should consist of alcohol, 1 part ; water, 10 parts. 



If the object is small or of moderate size it may be left in the above 

 twenty-four hours, then transferred to a mixture of alcohol, 1 part ; 

 water, 3 parts, or to a mixture of alcohol, 1 part ; water, 2 parts, ac- 

 cording to the consistency of the object, and in which it may remain for 

 two or three days and then be transferred to alcohol, 2 parts; water, 1 

 part, and, after a day or t wo, into 95 per cent, alcohol, Jf_the specimen 

 is intended for histological purposes. 



S. Mis. 40—39 • 4Vi^^»>d <A 



