GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. xxxiii 



time, however, many colouring agents are employed ; specimens 

 may be stained with tincture of saffron, with anilin, with 

 indigo-carmine, hoematoxylin, and picric acid ; and also with 

 nitrate of silver, chloride of gold, chloride of palladium, and 

 perosmic acid. 



When fresh membranes are to be acted on by nitrate of 

 silver or chloride of gold, the pieces should be cub from the 

 living animal, and thrown into the solution without further 

 preparation. The solution should be kept in a dark place as 

 long as the action is allowed to proceed : the preparation 

 should then be recovered by means of sharp-pointed glass rods, 

 washed, and placed in the light. 



After fragments of tissue are taken out of solutions of silver, 

 they may be placed in alcohol or glycerine, and then exposed 

 to light ; or the specimen may be prepared for microscopic 

 examination in glycerine, and allowed to remain in it for 

 twenty-four hours. Preparations which have been in solution 

 of chloride of gold, after having been thoroughly impregnated 

 with it, should be placed in water slightly acidulated with 

 acetic acid. 



If the action is required to be more intense, the membrane 

 is to be well brushed, before it is removed from the staining 

 fluid, with a wet brush. This is the best method of procedure, 

 for example, with the centrum tendineum of the rabbit, 

 which should be thus brushed both on the abdominal and on 

 the thoracic surface, whilst the cornea need only be brushed on 

 the anterior surface, and then removed from the liquid. 



In non-membranous tissues, just as in those which require to 

 be broken or cut up for microscopical examination, the pre- 

 pared specimen may be tinted whilst on the slide, after which 

 it may be washed, and then covered in the usual manner. 



Solutions of colouring matters which only act on the fresh 

 tissues, as, for example, nitrate of silver, can obviously only be 

 applied to sections made from recent and therefore necessarily 

 frozen tissues. On the other hand, colouring agents which, like 

 carmine, do not affect the fresh tissues, can only be applied to 

 sections which have been made from dried specimens, or from 

 those which have been hardened by chemical reagents. The 

 particular mode of treatment adapted to each tissue will be 



D 



