CHAPTER XXIX. 365 



(c) Staining with osmic acid in solution or as vapour. 



(2) In frozen sections, material fixed in formol : 



(a) Examination in polarised light. 



(b) Staining with Sudan III. or Scharlach R. 



(c) Staining with Nile blue. 



(d) Repeat (b) and (c) after immersing sections in cold acetone 



or cold alcohol for a few minutes. 



(3) In paraffin sections : 



(a) Fixation in osmic acid. 



(b) Fixation in bichromate osmic acid mixtures or fixation in 



bichromate solutions and post-osmication. 



(c) Prolonged fixation in bichromate and staining with 



Sudan III. (Ciaccio, Bell). 



(d) Staining with hsematoxylin (Weigert, Lorrain, Smith, 



Dietrich). 



(e) Treatment with chrysoidin and subsequent fixation in 



bichromate (Martmotti). 



Such a plan of investigation refers especially to vertebrate 

 materials, but with certain small modifications is applicable to 

 the study of fatty substances in developing eggs, embryos, and to 

 the tissues of invertebrates. Paragraphs 1 and 3 are both applicable 

 to invertebrate tissues and embryos, while in the case of para- 

 graph 2 the tests can be used after the whole embryos or eggs have 

 been fixed in neutralised and suitably diluted formalin. It should 

 be remembered that in all animal cells (and possibly plant cells, too) 

 there exist two categories of cytoplasmic inclusions, Golgi apparatus 

 and mitochondria, which are partly formed of lipoid materials, 

 and which we now know may produce fats, or may metamorphose 

 into fats. In nearly all eggs where fat granules are present, exami- 

 nation has revealed the fact that such " yolk " is derived either from 

 Golgi elements or mitochondria (GATENBY and WOODGER, Journ. 

 Roy. Micr. Soc. } 1920), and in certain cells of vertebrate tissues we 

 know that mitochondria may change into fat (MURRAY, Scientific 

 Report Cancer Research Fund, 1919). 



Reference should be made to the sections on ' Mitochondria," 

 "Golgi Apparatus," "Fat," and "Yolk" ( 673713), and 

 especially to the tables in 702, 708, 710 and 712, where some 

 attempt has been made to illustrate the behaviour of the various 

 inclusions after the application of certain well-known techniques. 

 It is always necessary to ascertain exactly the condition and 

 behaviour of the mitochondria and Golgi apparatus in tissues or 

 cells being investigated for fatty and lipoid substances, particularly 



