XIV, 2. Eisen: Notes on fixation, stains, the alcohol method, etc. 197 



hour's immersion in the water. Testes fixed in either of these irid- 

 ium rnixtures give süperb figures. Tlie method offers two advan- 

 tages over any others with which I am aequainted, viz : the ra- 

 pidity with which the tissues are washed out in water, and the 

 perfect and equal preservation of all the cells, eveu those nearest 

 the margin. I have tried tliis fixative on a number of other 

 Salamander tissues with equally fine result. For Oligoeha't;e these 

 mixtures are less suitable, as they cause the tissues to stain too in- 

 tensely, and I have not yet had time to experiment with lnodifications, 

 which, however, I have 110 doubt will be found. For Salamander 

 embryos and larvse this fixative is espeeially to be recommended. 

 I drop the larvse directly into the fixative, without previous killing, 

 and obtain most admirable results. 



The alcohol method. 



I believe it is generally accepted almost as an axiom that the 

 alcohol and distilled water methods for fixing paraffin sections to 

 the slides are unsatisfactory, when serial sections are required. Both 

 from text books and from private complaints, I hear of failures, 

 the sections now and then floating away. I have for two years used 

 a modified alcohol method with splendid results, and I believe that 

 during all that time not a dozen sections have floated off. The 

 method, as I use it now, is quick and sure, and in my opinion pref- 

 erable to any other when thin sections , 4 to 8 ju, are used. The 

 following stages of this method must be closely observed : 



1) The slide is flooded with alcohol of 80 per cent., if it is desired 

 to affix sections made with paraffin melting at 54° C. Stronger alcohol 

 will evaporate too quickly, weaker might cause the paraffin to becoine 

 overheated and to melt, which would cause shriukage and ruin. 



2) The paraffin sections are spread on the alcohol and slide 

 and removed to the shelf, top, or side bench of the paraffin bath. 

 The water in the bath is kept at 55° C. and the surface of the 

 bench is one or two degrees less. The paraffin sections will at once 

 Stretch out but will not readily melt, the low temperature pre- 

 venting it. The alcohol would have to boil before this could happen. 

 Still this part of the process must be watched most carefully and 

 the slide must be removed the very moment the sections are fully 

 stretched. This requiers only a few seconds time. 



