Preparing Vegetable and Animal Tissues. 435 



Method J) — continued. 



ready to be placed in the imbedding box, and 

 also to avoid heating the copper lifter or the 

 needles too much. Tissues thus imbedded may 

 be kept unchanged for any length of time. 



To get perfectly satisfactory results, the tissue we are 

 treating must be living ; smaller vegetable objects, as flower 

 buds, ovaries, growing apices, &c., must be dropped into the fluid 

 as soon as separated from the plant, and animals hke tadpoles, 

 worms, and larvce are placed directly into the fluid, where 

 they are killed rapidly and in an extended position. Tissues 

 of plants and animals must be placed in the fluid as soon 

 as separated by dissection. Tissues of warm-blooded animals 

 should be placed in the picro-corrosive alcohol of correspond- 

 ing warmth. Treating tissues hke brain, it is best to place 

 into the bottom of the vessel a pad of cotton-wool or felt to 

 allow the hardening fluid to penetrate readily ; the pad must 

 be removed before the chloroform-alcohol is placed below the 

 tissue. My method was found to give very satisfactory 

 results with plasmodia of myxomycetes, growing apices, 

 developing endosperm, stem and leaf structures, human foetal 

 brain, frog's cartilage, muscle, myxomatous tissue, retina, 

 tadpoles, wasp larvae, caterpillars, &c. Karyokinetic figures 

 are specially well fixed, and show the minutest details. 



Now, a few words as to mounting sections. Sections cut 

 in ribbons (I use the Cambridge rocking microtome) are 

 fixed to a slide by Schallibaum's method, thus : — An even 

 layer of the fixing material is spread on the slide, the shde 

 heated to 30° C. (melting point of paraffin = 46° C), and a 

 piece of the ribbon gripped by a pair of forceps at one end 

 and quickly laid down on the warm slide. In this way I 

 get the sections to lie perfectly flat, and it is even possible 

 to make a closely coiled-up ribbon expand with the greatest 

 ease, without causing any further trouble. The slide is next 

 heated above a Bunsen, just enough to melt the paraftin ; it is 

 then placed in a vessel containing resinified turpentine, which 

 latter removes the paraffin in a few minutes ; the turpentine 

 is removed by absolute alcohol, and the sections stained by 

 any of the current methods, then dehydrated in absolute 

 alcohol, cleared in resinified turpentine, and, lastly, mounted 

 in Canada balsam dissolved in turpentine, as tui'pentine- 

 balsam has a low refractive index. 



