CHROMATIN, ANIMAL CHROMOSOMES, NUCLEOLI 257 



and which allows normal living cells and tissues to be studied 

 under the highest powers of the microscope. The original 

 chamber has been modilicd and improved in various ways by 

 Clark and others {Anat. Rec, xlvii, 1930, p. 147). INIore recently 

 Abell and Clark [Anat. Rec. liii, 1932, p. 121) have developed an 

 apparatus which makes it possible to introduce fluids into the 

 chamber and thus to study the effects of various substances on 

 the living cells. 



Baumgartner and Payne {Jour. Exp. Zool., lix. 1931, p. 359) 

 have devised a simple method of studying the spermatogenesis of 

 the grasshopper in the living animal. The insect is first anaesthe- 

 tised, and then the wings and the hind legs are removed at the 

 autonomous joint, and a rectangular opening is made in the left 

 side of the abdomen, from and including segments 2 to 4. The 

 specimen is now placed on a glass slide, the right side down, and 

 melted parafBn is run, from a pipette, over the antenna?, the legs 

 and around again to the head leaving a space about twice the 

 width of the animal along the dorsal side. The basin thus formed 

 is filled with Ringer's solution (cold-blooded formula), and the 

 testis is quickly pulled out into it, the yellow membrane removed 

 and a few follicles are secured by a fine thread which is anchored 

 to the paraffin. A coverslip is now placed over the basin and 

 sealed with the paraffin to prevent evaporation. 



While tissue cultures offer almost ideal material for studying 

 living cells, there are several simple and satisfactory methods of 

 preparation which will allow one to observe excised living cells 

 unchanged for a number of hours. When the cells of a tissue are 

 easily dissociated {e.g. the spermatocytes of insects) they can be 

 mounted in normal body fluids, such as lymph, and examined by 

 the hanging drop method. Since such fluids may undergo rapid 

 changes on removal from the body, it is better, perhaps, to 

 employ some " indifferent " medium for mounting. BfiLAit, who 

 worked extensively with the spermatocytes of grasshoppers, 

 recommends Ringer's solution (cold-blooded formula) or 

 Tyrode's* solution {Zeitsch. f. wiss. Biol., Aht. D, cxviii, 1929, 

 p. 359). The method is generally applicable to all tissues provided 

 an isotonic Ringer's solution is used, i.e., for warm-b9ooded animals 

 use the corresponding formula. Belar has called attention to a 

 number of desiderata in the successful application of this method, 

 (For a full account see Methodik der wissenschaftlichen Biologie, 

 i, 1929, p. 641). Among these the following are to be noted : 



It is essential that the distilled water used be free from the salts of 

 the heavy rnetals and for this reason distillation from glass retorts 

 and condensers is recommended. In removing tissue from the 

 host, and in the subsequent manipulations, great care must be 

 exercised to prevent the loss of water by ev^aporation. Cells may 

 be dissociated from the tissue by teasing with clean needles, or in 



VADE-UKCUM. * §§ 780, 1430. ^ 



