114 Transactions of the Society. 



those in (a) being fixatives causing the maximum disturbance and 

 destruction in the cell, those in (c) the least. 



{a) Carnoy, Petrunkewitsch, alcohol, Gilson, picro-nitric, etc. 



Tat, mitochondria, Golgi apparatus, and often early yolk discs 

 do not show after these. (Using alcohols and xylol subsequently.) 



(h) Bouin, Zenker, corrosive acetic, Flemming-with-acetic 

 acid, etc. 



Mitochondria and Golgi apparatus rarely show after these, 

 except possibly in mammals, where these cell inclusions are more 

 resistant than in invertebrata. 



(c) Osmic acid, Flemming-without-acetic, Champy, Altmann, 

 formalin, Mann's mercury-osmic liquid, Sjovall's method, etc. 

 Preserve everything (except glycogen ?) (Using Huids subsequently 

 as above.) 



In section (c) the formol alone vvill not preserve fat ; but see 

 Sjovall's method above. 



The fixatives have not been classed according to how they 

 themselves alone affect the contents of the cell, but according to- 

 how they preserve the cell preparatory to its treatment in the- 

 liquids necessary for embedding and sectioning. 



Injurious liquids which should never be used in fixation are 

 acetic acid, chloroform and alcohol. Acetic acid is certainly 

 most destructive to delicate lipins, and its use, except where 

 chromosomes are being studied, is rarely indicated ; any worker 

 who uses acetic acid in his fixing mixtures cannot hope to get 

 a correct picture of any part of his cell, possibly excepting 

 the chromosomes (not the resting nucleus). The most valuable 

 fixatives are osmium-tetroxide, chromium-trioxide, bichromate of 

 potassium, and formaldehyde, in the order named. The most 

 valuable mixtures are Miiller-formol, Plemming-without-acetic,. 

 Altmann, and Champy ; the three latter approach as near perfection 

 as present-day technique allows. Altmann's fluid (KaCraO: -f OSO4) 

 I find to be a splendid mixture. In no case, except in small 

 invertebrates, do these fixatives (excluding formol) give a true 

 fixation of cell aggregates ; this is due to their inferior penetrating 

 powers, and to an unevenness of penetration. Small invertebrates,, 

 both marine and fresh- water, and small pieces of tissue, are usually 

 exquisitely preserved in chrome-osmium mixtures, but are not then 

 generally suitable for staining and mounting whole, especially for 

 staining in carmine mixtures. 



Stains 



Staining methods, which are now being used with conspicuous 

 success on problems connected with the finer structure of the cell,, 

 are as follows : — Iron-haematoxylin, Altmann's acid fuchsin and 

 picric acid, Benda's alizarin and crystal- violet (.?), Kopsch (OSO4) 



