286 CYTOLOGICAL METHODS. 



with a knife wetted with alcohol. Bring the sections into 

 water, and stain with safranin or gentian for twenty-four 

 hours or more, or (for the achromatic figure) with Delafield's 

 haematoxylin. Mount in damar. 



Flemming prefers not to imbed by penetration in paraffin, nor to employ 

 any other of the infiltration methods of imbedding, because he finds that 

 these methods may be somewhat injurious to cells unless great care be taken. 

 I myself have not been able to discover any deformations or other erroneous 

 appearances that can be attributed to the paraffin method, and think that it 

 may legitimately be employed, using cedar oil for clearing, and using a soft 

 paraffin so as to be able to imbed at the lowest temperature possible. 



RABL'S Method (Morph. Jahrb., x, 1884, p. 215) is nearly the 

 same. He fixes in the chromo-formic mixture or in platinum 

 chloride for twelve or twenty-four hours, washes out, and treats 

 for twenty-four to thirty-six hours with alcohol of 60 to 70 

 per cent., and then with absolute alcohol, and stains sections 

 with safranin or hsematoxylin, or with both. This is done by 

 first staining very lightly with dilute Delafield's haematoxylin, 

 and then with safranin. This he rightly claims to be perhaps 

 the most beautiful stain that can be produced. He advises 

 that green light (which can be obtained by means of a green 

 glass stage-plate) be used to work with (see the paragraph 

 on Green Light in the Appendix). 



STEASBUEGEE'S Methods (see Arch.f. mik. Anat., xxi, 1881, p. 477). 



USZOFF'S Nitric Acid Method (see Arch. f. mik. Anat., xxi, 1882, 

 p. 292). 



PFNITZEE'S Sulphate of Soda Method (see Morphol. Jahrb., xi, 1885, 

 p. 54). 



607. The " Nebenkern" (or " Sphere Attractive/' or " Archo- 

 plasmakugel "). The best objects at present known for the 

 study of this element are the ova (segmenting) of Ascaris, and 

 the sperm-cells of Helix, or other Pulmonata. 



In the ova of Ascaris it is best demonstrated, according to 

 VAN BENEDEN and NEYT (Nouv. Rech. sur la Fecond. et la Dtv. 

 mitosique), by fixing with acetic alcohol (ante, 603), and 

 bringing the ova into one-third glycerin in which is dissolved 

 a little malachite green. The " spheres attractives " stain 

 green. See also BOVERI'S Zellen-Studien (in Jen. Zeitschr.f. 

 Naturw., xxi, 1887, p. 423, or sold separately). 



The " Nebenkern " of the sperm-cells of Pulmonata should 

 be studied both living and in sections. According to my ex- 



