364 CONNECTIVE TISSUES. 



referred to as revealing the essential similarity of Weigert's method 

 for the myelin sheath of nerves and Altmann's method for mito- 

 chondria. The staining reactions of the Golgi apparatus blacken- 

 ing after prolonged action of osmic acid, staining with hsematoxylin 

 after prolonged mordanting with bichromate suggest that it is 

 made up of fatty substances, and, further, that these substances 

 are not readily oxidised. They thus correspond in their behaviour 

 to lipoids such as cholesterin. 



From what has been said, it is clear that for the study of fatty 

 substances several methods must be applied to the tissues. 



In so far as the selection of a fixative is concerned, it follows 

 that fixatives containing alcohol or chloroform must be avoided. 

 A fixative such as Carnoy, or such mixtures containing strong 

 alcohol or chloroform, are themselves fat solvents, as well as lipoid 

 solvents, and they dissolve away all fat-vacuoles and shrink up 

 cell organs which may be formed partly of other ' fatty ' sub- 

 stances, e.g., mitochondria. Other fixatives, such as picric acid or 

 corrosive sublimate, while in themselves not fat or lipoid solvents, 

 are unable to prevent the fat from being dissolved away in any 

 subsequent dehydration and clearing of the tissue. Very few reagents 

 are known which are able to form with fat substances insoluble 

 or scarcely soluble in alcohol and a clearing medium, like xylol ; 

 osmium tetroxide and, to a less extent, potassium bichromate, 

 are thus valuable reagents to the histologist. Various oils act 

 differently towards these fat Os0 2 compounds ; xylol and chloro- 

 form do not easily disintegrate them, but an oxidising oil like tur- 

 pentine-will quickly do so. The " compounds " of Os0 4 with fats 

 and lipoids are ill understood, but Partington and Huntingford 

 have recently shown (see 772) that the reduced black substance is 

 a hydrated form of Os0 2 . 



Martinotti (see 772) has recently introduced a new method 

 which may prove of great importance. According to this observer 

 the orange yellow dye chrysoidin (phenyl-azo-m-phenylene-diamide), 

 when applied to fatty tissue and then treated with an oxidising 

 agent, such as bichromate of potash, has the power of preventing the 

 fat globules from being dissolved away in alcohol, benzol and xylol. 

 In preparations the fat looks a brown orange colour. 



A complete histochemical investigation of fatty cell inclusions 

 comprises, thus, the following methods :- 



(1) In fresh preparations : 



(a) Examination in polarised light. 



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



