BOTANICAL MICROTECHNIQUE. 



been uniformly acted on by the fixing fluids, those parts 

 which lie nearest the cut surfaces deserve, in general, the 

 greatest confidence in their study. 



33. If the objects to be fixed are very light, they can be 

 easily attached by strips of filter-paper to the bottom of the 

 vessel containing the fixing fluid. Especially with objects 

 which are with difficulty wetted, it is often useful to inject 

 them with the fixing fluid, which is easily done by the aid 

 of a filter-pump. 



It is not possible to give general statements as to the 

 time necessary for complete fixing. This depends, aside 

 from the size of the object, primarily upon the character of 

 the fixing fluid used, and sufficiently exact statements on 

 this point will be given in the description of the different 

 methods. 



So, too, the quantity of fluid to be used varies much. In 

 general, one needs relatively little of the energetic fluids, 

 like those containing sublimate, for example ; while, espe- 

 cially where potassium bichromate is employed, the use of 

 large quantities of fluid is recommended. 



34. For the fixing of objects which easily turn black 

 Overton (I, 9) recommends alcohol containing sulphurous 

 acid. He prepares this by adding to gram of sodium sul- 

 phite (Na 2 SO 3 ) a few ccm. of 80$ sulphuric acid and con- 

 ducting the fumes of sulphurous acid which arise, directly 

 into 100 grams of alcohol. Picric acid dissolved in water or in 

 30 to 50$ alcohol may be combined with sulphurous acid in 

 the same way. In preparations treated with the fluids named, 

 the finest protoplasmic differentiations are preserved, and 

 staining with haemotoxylin or carmine succeeds finely. 



B. REMOVAL OF FIXING FLUIDS. 



35. It is necessary, in general, before staining to remove 

 completely the fixing fluid used. The fluid to be used for 

 this washing of the preparation depends upon the character 

 of the fixing medium. If this is readily soluble in water, it 

 is best to use running water, and for this purpose the drain- 

 ing-boxes recommended by Steinach (I) are well adapted, as 



