GOLGI BODIES ETC. 303 



and sometimes supplied in laboratories, is not good for cytology. 

 For some reason old solutions of silver nitrate will not always 

 work properly. Old reducer is useless. It should be remembered 

 that there is no recognised intra-vital stain for the Golgi apparatus. 

 The globules rch ich sometimes stain up ivith neutral red are not the Golgi 

 apparatus. It is much better not to endeavour to investigate the 

 cytoplasmic inclusions of Protozoa until one has had some 

 experience with Metazoa. It is safer to study some vertebrate 

 and mollusc or insect material first. It should be noted that in 

 many cases both mitochondria and Golgi bodies can be seen in 

 the living cell {e.g. mollusc or insect germ cells) — this will be the 

 surest index of their actual shape and size. Living cells are best 

 examined in the natural fluid of the animal, but if this is not 

 possible, refer to § 1430, where various suitable media are 

 mentioned. 



690. Advances in the Techniques since 1928. Reference to 

 cytological memoirs dealing with the cytoplasmic inclusions, 

 shows that the methods have largely become stereotyped to Da 

 Fano, Kolatchew, Weigl, Regaud-acid fuchsin, and Champy iron- 

 alum hematoxylin. Some workers have depended solely on 

 Weigl or Kolatchew, and Regaud alum hsematoxylin or acid 

 fuchsin. The last two methods, namely pre-fixation in chrome- 

 osmium or corrosive-osmium followed by post-osmication and 

 fixation in Regaud's chrome-formalin followed by alum h;rmat- 

 oxylin or acid fuchsin, will certainly cover most of the ground, 

 but there are some recent improvements which could be noted 

 with advantage. Firstly, the formalin and chrome-fixatives 

 should be made isotonic : while this may not improve the fixation 

 of surface cells, it will give a larger amount of material for study. 

 Second, F. Aoyama's* modification of Cajal, is undoubtedly an 

 improvement on Da Fano, which has gradually ousted Cajal's 

 method. Third, our ideas on the subject of the microehemistry of 

 fats have had to undergo considerable change. Cytologists should 

 consult Chapter XXVIII for a modern report on this subject, 

 which is of major importance for them. 



691. Chrome-osmium Techniques. Potassium bichromate or 

 chromium trioxide, used in watery solutions, will not alter 

 true fats in such a way that full vacuoles of the latter will 

 appear in finished sections prepared by routine methods ; but 

 combinations of such salts with osmium tetroxide provide 

 fixatives which will preserve almost all cell elements in finished 

 sections. It should he carefully noticed that the long osmication 

 of the Weigl-Kopsch method will not always prevent fat globules 

 from being dissolved out by xylol alcohol used for clearing and 

 mounting. Such preparations when being used for studies of fats 

 must be mounted in Farrants' or some such watery medium 



* Refer to 730a, also. 



