17 



Preservatives 



Decimal Divisions Used in Chapter 



P 00 GENERALITIES 



01 General observations 



02 Method of arrangement of formulas 

 P 10 FORMULAS 



11 Solutions of inorganic reagents 

 11.1 Formulas 



12 Organic- reagents 



12.1 Alcohols, aldehydes, ketones 



12.2 Phenols, and mixtures containing phenol and phenol derivatives 



12.3 Other organic reagents, including mixtures 12.1, 12.2 



13 Other preservatives, including mixtures of 11 and 12 

 13.1 Formulas 



P 00 Generalities 



P 01 General Observations 



The distinction between preservatives, 

 fixatives, and mountants is difficult to draw 

 and has not always been observed in 

 biological literature. As used in the 

 present work, a preservative is distin- 

 guished from a mountant only in that the 

 latter will hold the coverslip in place of its 

 own accord, while the former requires 

 that the coversHp be sealed in position by 

 one of the methods described in Chapters 

 2 and 3. It does not, for example, appear 

 justifiable to the writer to refer to the 

 well-known lactophenol of Amman (P 12.2 

 Amman 1898) as a mountant, since it can- 

 not be used for the preparation of jierma- 

 nent slides unless the edge of the coverslip 

 is sealed. The distinction between preserva- 

 tives and fixatives is more difficult to draw, 

 but the author has endeavored to group in 

 the present place all those fluids which are 

 most usually employed for the actual 

 preparation of a wholemount, or for the 

 storage of material, as distinct from those 

 fluids which are employed for the fixation 

 of material before mounting or sectioning. 



When the writer has been in doubt he has 

 given a cross reference both in Chapter 18 

 and in the present chapter. 



Probably the most widely used pre- 

 servative today is a simple dilution of 

 formaldehyde, opinion varying as to the 

 exact concentration which may be em- 

 ployed. Certainly the 4% formaldehyde 

 solutions (the so-called 10% formalin so 

 commonly referred to in the literature) is 

 far too strong for the preparation of a 

 microscope slide, and a dilution to at least 

 H of this concentration is perfectly ade- 

 quate to prevent the growth of micro- 

 organisms in a sealed preparation. Alcohol 

 by itself is practically worthless because 

 of the difficulty of sealing it under a cover- 

 shp. Various mixtures of alcohol, glycerol, 

 and formaldehyde have, from time to time 

 been employed, however, and are given 

 below. 



P 02 Method of Classification of 

 Formulas 



The fornudas given below have been 

 grouped according to their usage as much 



175 



