250 THE AMERICAN MONTHLY [Sept., 



Microscopical Technique Applied To Histology. — III. 



[from the FRENCH OF RENE I50NEVAL.] 



{Continued from page 80.) 

 METHODS OF EXAMINING MEMBRANOUS OBJECTS. 



Til ere are no more instructive preparations than those of 

 membranous objects after fixing and staining 



1. Fixation in the Normal Position. — The best way is to 

 fix the membranes without disarranging them from the position 

 occujiied during the life of the animal. Unfortunately this is 

 applicable to only a very limited number of cases. Use a fix- 

 ing reagent that acts very rapidly and produces no contraction. 

 Picric acid and bichloride of mercury may be selected, but osmic 

 acid is preferable, and, whenever possible, as vapor, otherwise in 

 a one per cent solution. The time of action varies from 2 to 10 

 minutes. . . . Remove a small piece, wash for 20 minutes, stain 

 in picro carmine, or with hiematoxylin and eosine 



2. By Partial Drying (Ranvier's method). — Extend the 

 membrane upon a glass })'ate by the fingers applied at the mar- 

 gins. While it is moist, it will contract the moment it is left to 

 itself, but when beginning to dry (and on account of the heat of 

 the fingers it tends to dry quicker at the edges), its margins ad- 

 here to the glass, and by extending it on all sides it may be 

 completely spread out. Fix by absolute alcohol or by picric or 

 osmic acid. Wash and stain 



3. Membranes Forming Close Cavities. — . . . With 

 a syringe inject the fixative (alcohol or picric or os-mic acid) 

 into the cavity. Tie it beyond the canula and put the distended 

 membrane into the fixing solution. In a few hours the fixation 

 is perfect; cut the membrane, wash, stain. The lungs, the blad- 

 der and the digestive canal of batrachians should be treated 

 in this way. 



METHOD OF DISeOCIATION. 



When we have learned the arrangement of the elements by 

 sectioning, we cannot often positively observe the form of the 

 cells or their intimate connections. Then we have recourse to 

 dissociation, that is, to processes permitting the isolating of the 

 elements from one another. The instruments needed are curved 

 scissors, .... straight needles, two fine forceps, .... a plate 

 of glass with strips of black, white, green, and red jjaper beneath 



