104 . Transactions of the Society, 



Fats and Oil. 



Oil is a popular name for fats which are liquid at room 

 temperature. The fatty tissue of animals consists nearly, if not 

 always, of a mixture of the three fats — stearin, olein and palmitin. 

 Stearin and palmitin belong to the saturated series, while olein 

 being unsaturated has the property of reducing osmium tetroxide, 

 and so producing the well-known black colour familiar to all who 

 have used osmic fixatives ; this property is not shared by untreated 

 fresh palmitin or stearin, but the reduction of osmium tetroxide can 

 be induced in various tissues and cell materials by previous treat- 

 ment in formalin. The blackening effect of osmium tetroxide can 

 take place in the presence of a chrome compound, such as chromium 

 trioxide (chromic acid), a point the importance of which will appear 

 later.* Various oils have varying olein content, or olein may of 

 course be absent altogether ; olive oil, for instance, is largely olein, 

 and is turned by osmic acid a black colour ; according to the olein 

 content the oil droplet after treatment in osmic acid may be dark 

 yellowish, brown, to black. As has already been noted, fats are 

 soluble in acetone and xylol, but not after treatment in osmic 

 acid. Vacuoles with a partial coagulum (fig. 1) are possibly caused 

 by the incomplete washing out with alcohol or xylol of a mass 

 partly preserved in the osmic chrome fixative used. 



Bolles Lee {3) mentions that apart from the black effect pro- 

 duced in the fresh tissues by osmium tetroxide and olein or oleic 

 acid, palmatin and stearin or their acids may be " browned " by 

 OSO4, and subsequently turn black after treatment in alcohol. This 

 is the view of Altmann, Starke and others ; but Mann {1) considers 

 that quite pure palmitin and olein would not blacken with osmium 

 tetroxide, and that any after-blackening effect got with alcohol is 

 due to a reduction and hydration of the OsO^ into Os(OH4) by 

 means of the alcohol, and not of the fats. These opinions are of 

 small importance to the zoologist, because in nature the three fats 

 are nearly always present in any adipose tissue. 



With these explanatory remarks on lecithin and fat I may now 

 proceed to give tables which are planned to assist in the identifi- 

 cation of those cell- bodies which are met in developmental stages 

 of the organism. The tables are drawn up for the usual methods 

 of the zoologist when preparing sections — that is, fixation in one 

 or more of the commoner solutions : — Flemming, Carnoy, Petrun- 

 kewitsch, Bouin, formol, Miiller, Champy, corrosive acetic, Perenyi, 

 etc., passed through alcohols of different strengths, cleared in xylol, 

 chloroform (not turpentine) oil, embedded either in celloidin or 

 paraffin wax or in both, sectioned, and then stained. More will 



* Compare IMarchi method for degenerate nerve. 



