300 GOLGI BODIES ETC. 



685. Choice of Method.* We have given below a number of 

 methods for Hpoid granules, mitochondria, and other cell inclusions, 

 and not all are suitable for every piece of work. It is very rare 

 to find that one single method will produce the same good result 

 in both vertebrate and invertebrate tissues. In the same way, 

 methods which act satisfactorily with amphibia will often give 

 disappointing results with mammalia. Osmic-cln"ome fixation 

 will nearly always be found excellent for all classes of inverte- 

 brata ; Flcmming- without-acetic acid and Champy-Kull can be 

 highly recommended. For amphibia the addition of some 

 KaCraO^ to the Flcmming is necessary before a correct fixation 

 of the mitochondria is obtained ; thus Champy's fluid was 

 invented for amphibia and gives very satisfactory results (§ 49). 

 For mammalian tissues a prelitninary fixation in osmic acid 

 fixatives is not generally indicated ; the tissues of mammals 

 are far more " fatty " than those of invertebrata or amphibia, 

 and one finds that the OSO4 becomes reduced very rapidly and 

 penetration is very poor. For mammalian tissues formalin- 

 chrome (Regaud, Bensley-Cowdry), formalin-corrosive or formalin 

 alone are indicated as a preliminary treatment. Formalin does 

 not destroy lipoids, and by subsequently placing small pieces of 

 chrome-formalin fixed tissues in osmic acid (post-osmication), a 

 fixation of lipoids and fats is obtained (Schridde) ; the same 

 result may be got by fixing tissues in chrome salts and then 

 transferring the osmic acid. It should be noted, however, that 

 previous fixation in a chrome salt often prevents the blackening 

 of the Golgi apparatus unless the chrome salt is well washed out 

 of the tissues, and the osmication is prolonged ; the methods of 

 Nassonow and Ludford should be used when an impregnation of 

 the Golgi apparatus is required by means of an osmic method, 

 but the formalin silver nitrate methods of Aoyama and Da 

 Fano are always clearly indicated for work on the Golgi apparatus 

 of mammalian tissues. Fixation of tissues in the fluid surrounded 

 by crushed ice should be tried (§ 626). So far as possible intra 

 vitam and fresh smear preparations should be used, as these 

 nearly always give valuable results. 



686. Specificity of Techniques for Cytoplasmic Inclusions, Fats, 

 and Lipoids. As a rule the lipoid granules, vacuoles, and cell 

 organs containing fats or lipoids are formed, not of one pure 

 substance, but of a mixture of several. Consequently it is neces- 

 sary to proceed with caution in claiming a specificity for the 

 techniques for various lipoid substances : properly used, however, 

 these methods may give valuable evidence as to the precise 

 nature of any special body : micro-chemical methods, which 



* The beginner is recommended to master such techniques as those 

 of corrosive acetic and borax carmine, or Zenker and EhrHch's haema- 

 toxyhn, before trying these methods. 



