164 



SUMMARY OP CURRENT RESEARCHES RELATING TO 



exposed to any pressure, (2) the knife does not become blunt soon, 

 as it does not come in contact with the upper plate, as is the case with 

 Eanvier's microtome. 



Imbedding in Celloidin.*— Dr. C. S. Minot advises that after 

 dehydration in alcohol, the object should be placed for twenty-four 

 hours in a mixture of equal parts of absolute alcohol and pure ether 

 before immersing in the thin solution of celloidin. In this it 

 remains for from one to three days, according to the size of the 

 object, and is then imbedded in a thicker solution of celloidin. 



This is best done as follows : A cylindrical cork of convenient 

 diameter is selected ; a strip of glazed paper wrapped round it 

 tightly and fastened with a couple of pins as indicated in fig. 40. In 

 the box thus formed the object is placed and the celloidin poured 

 carefully over it. If necessary the object can be secured in any 

 position by pins. Bubbles will rise from the cork and interfere 

 with the imbedding ; two precautions will essentially diminish this 

 danger : 1. Pour in so much celloidin that it covers the object half an 

 inch deep, giving an opportunity for the bubbles to rise above the 

 tissue ; 2, Before imbedding, cover the end of the 

 cork with a thin layer of celloidin, which is allowed 

 to dry on completely. After the object is covered, 

 the cork is mounted on a lead sinker, and allowed to 

 stand until a film has formed on the upper surface. 

 It is then immersed in alcohol of 82-85 per cent, 

 (stronger alcohol attacks the celloidin) for one to 

 three days. The sections have to be cut under 

 alcohol. 



For mounting sections with celloidin left on 

 them. Dr. Minot has found none of the methods 

 hitherto recommended satisfactory, but after trying 

 various reagents, considers chloroform the most con- 

 venient medium of transfer from alcohol to balsam. 

 In using it, care must be taken to place the section 

 for half a minute in perfectly fresh alcohol, which 

 is really 95-96 per cent. ; if this is done, chloroform 

 will clear it up almost immediately. When the 

 section is in chloroform on the slide, the mounting 

 must be expeditious, and the balsam added while the 

 chloroform is still covering the section. The transfer, particularly of 

 a large section, from the spatula to the slide, with chloroform, is 

 often very difficult. To mount a single section, put it in alcohol on 

 the slide, wash with a few drops of fresh strong alcohol; let most of 

 the alcohol drain off, but while the section is still covered with it 

 add chloroform, drain off the mixture, and pour over the still moist 

 section a fresh dose of chloroform ; if the washings have been really 

 thorough, the sections will clear at once. 



With regard to the paper-box. Dr. E. G. Hebb tells us that he 

 has always used pill-boxes made of white board or of willow-wood. 



COM 



* Amer. Natural., xix. (1885) pp. 828-9 (1 fig.). 



