268 CHROMATIN, ANIMAL CHROMOSOMES, NUCLEOLI 



stuck through the corners of the cloth and on into a cork. The 

 cork, with the tissue hanging down beneath, is floated on the 

 surface of any sort of cyHnder, such as a graduated one of 500 or 

 1,000 c.c. capacity, containing 5 per cent, alcohol. Here the fixa- 

 tive will diffuse out of the tissue and go to the bottom of the 

 cylinder. After a few hours to overnight, the bag of tissue is 

 fastened to the wall of a shell vial with any ordinary paper clip, 

 and the dilute alcohol is gradually replaced by dropping in, with 

 a capillary syphon, 50 per cent, alcohol until a concentration 

 of about 40 per cent, is reached within the vial. During 

 this and the subsequent steps in dehydration, the fluid 

 within the vial is agitated either with compressed air, or 

 by a plunger. If the fluid which is being dropped into the 

 vial has a lighter specific gravity than that in the vial, the 

 former should be introduced by a small glass tube running from 

 the syphon to the bottom of the vial. After the tissue is in 40 per 

 cent, alcohol, a mixture of equal parts of anilin oil and 50 per cent, 

 alcohol is dropped in until saturation for the mixture is reached. 

 (Ordinarily, about 150 to 200 c.c. is passed through a vial of 

 about 25 c.c. capacity during the course of three or four hours. 

 Note : The mixture of anilin oil and alcohol may absorb enough 

 moisture, on damp days, from the atmosphere, to cause some of 

 the oil to be thrown out of solution and making the fluid within 

 the vial become cloudy. The addition of a few drops of 95 per 

 cent, alcohol will generally clear up the solution again.) Next, 

 a mixture of anilin oil and 70 per cent, alcohol (equal parts) is 

 added by the drop method. Then, in turn, comes pure anilin oil 

 and oil of wintergreen, the time taken to add each one of these 

 being about four hours. After clearing in wintergreen oil, the 

 tissue is removed from the cloth bag, which during the steps just 

 described has protected the tiny tubules from mechanical injury. 

 Imbedding is by steps, some seven to ten changes being used, thus 

 one part of paraffin to seven of wintergreen oil, etc. Painter has 

 found it very convenient to use, during imbedding, ordinary 

 Naples' staining jars, with Gooch crucibles which fit snugly into 

 the open top. The paraffin and wintergreen oil tend to separate 

 out on standing, so that each mixture must be well agitated before 

 use. The whole imbedding process should not take over two or 

 three hours. 



630. Avian Chromosomes. The methods given above for 

 mammals are generally applicable here. In the adult active testis 

 the tubule walls are very thin and the contents so fluid that on 

 rupture the germ cells tend to flow out into a solid mass, making 

 preservation difficult. One should either cut very thin slices of 

 the testis, or else tease bits of the testis directly in the preserving 

 fluid. In either case, great care should be exercised in the subse- 

 quent handling of the tissue so that the tubules lying on the 



