iTiH rili; A.MKKU'AN .MnN'niLV ISopt., 



Microscopic.il Tccliiiiiiuc Applied To Hislolo^v.— 111. 



1 1 KoM niK 1 UKNi 11 OK KKXK ItONKVAl..] 

 (Coiitinuai from i>age SO.) 



METH«)I\< OK KXAMIM.Nf. M KM liKA NOl S OIl.IKCTS. 



'riuTf arc no luoro instruotive |irc|»:irations than those of 

 iiMinhraimus ohjcots after fixinjj and staininjx 



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

 (i.\ till' nienibrani'S without <lisarran;iin<: tlieni from tlic jiosition 

 occupied during the life of the animal. Unfortunately thi.s is 

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

 inj; reagent that acts very rai)idly and produces no contraction. 

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

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

 a one ]>er cent solution. The time of action varies from 2 to 10 

 minutes. . . . Remove a small piece, wash for 2U minutes, stain 

 in picro carmine, or with Inematoxylin and eosine 



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

 membrane Ujjon a glass p'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. — . . . Witli 

 a syringe inject the lixative ( alcohol or ]iicric or osmic 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 sliould be treated 

 in this way. 



METIIon OK DISSOCIATION. 



When we have learned the arrangement of the elements by 

 sectioning, we cannot often jiositivel}' 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 paper beneath 



