CHROMOLIPOIDS 



65 



CHROMOSOMES 



adrenal, and are easily distiuguisliable 

 from carotinoids because they do not give 

 the color reactions with sulphuric acid 

 and iodine-iodide. From melanins they 

 are to be distinguished by not dissolving 

 in alkalies, by staining with sudanand 

 scharlach and by not reducing am- 

 moniacal silver nitrate. The following 

 method of Hueck is given by Lison : 

 Stain with nile blue. Treat the sections 

 for 24 hrs. with aq. dest. oxygenated 

 3% (= commercial hydrogen peroxide 

 diluted with 12 volumes water). This 

 leaves the chromolipoid:; blue, the mela- 

 nins decolorized. Lison concludes that 

 distinction from pigments of hema- 

 togenous origin is not so easy because 

 some chromolipoids contain iron. See 

 Lipids, tabular analysis. 



Chromophii (G. chroma, color and phileo, 

 I love), a loose term applied to almost 

 any granule, cell, or tissue which has a 

 pronounced affinity for stains. Baso- 

 philic cytoplasmic materials in gland 

 cells and in nerve cells (Nissl bodies) are 

 sometimes called chromophii, moreover 

 chromophii reaction is unwisely used to 

 designate the chromaffin reaction of 

 epinephrin producing tissues. 



Chrom-Osmic-Acetic fixative, see Lillie's. 



Chromosomes.— Written by A. R. Gopal- 

 Ayengar, Barnard Free Skin and Cancer 

 Hospital, St. Louis, Sept. 10, 1946— 

 These are discrete bodies usually con- 

 stant in number in the cells of a given 

 species and frequently having distinc- 

 tive structure into which the chromatin 

 material of a nucleus resolves itself 

 during the mitotic process (see Mitosis). 

 From a chemical standpoint the chro- 

 mosome is a protein fiber like silk or 

 hair, presumabl}'' depending on a pep- 

 tide chain linkage — C — C— N — . On this 

 structural framework the permanent 

 hereditary units, the genes (which may 

 be considered as the atoms of heredity), 

 are located at definite loci. In a sense, 

 therefore, the chromosome may be con- 

 sidered a giant molecule (Darlington, 

 C. D., Nature, 1942, 149, 66-69, Astbury, 

 W. T., Proc. 7th Int. Genet. Congress., 

 1939 (Camb.), 1940, 49-51). It is gener- 

 ally stated that the chromosomes of 

 sperm cells consist of basic proteins, 

 such as protamines or iiistones, in com- 

 bination with highly polymerized de- 

 soxyribose nucleic acid (Mirsky, A. E., 

 Advances in Euzymology, 1943, 3, 1-34). 

 Smear-Squash technique. The rapid 

 and spectacular advances in our knowl- 

 edge of cytology and cytochemistry 

 during the last fifteen years have 

 greatly altered our ideas of chromo- 

 some structure and behavior. Progress 

 in this direction has been possible 

 through the introduction of newer tech- 

 niques, such as smears and squashes, 



which have largely supplanted the 

 classical methods of paraffin sectioning. 

 In order to obtain the most satisfactorj' 

 results, it is imperative to employ cyto- 

 logical techniques calculated to bring 

 out iiue structures and details a.i 

 quickly and accurately as possible. 

 Most of the smear-squash methods, de- 

 spite their extreme simplicity, give 

 superior results because of instantane- 

 ous fixation and rapidity of staining and 

 finishing schedules. Moreover, it is 

 possible to examine thin layers of cells 

 or even isolated cells and their parts. 

 They are especially useful in the anal- 

 ysis of chromosome complexes and 

 associations and in the exact establish- 

 ment of numerical relations. Squash 

 preparations have special advantages. 

 Individual chromosomes can be recog- 

 nized more readily and easily, inter- 

 relations between chromosomes become 

 clearer, the preparations are almost 

 two-dimensional, which is of undoubted 

 value in chromosome measurement 

 since it obviates errors of measurements 

 due to differential focussing of three 

 dimensional structures. However, there 

 are a few disadvantages resulting 

 from the disturbances of the natural 

 relationships of the chromosomes. 

 These are more than offset by the merits 

 of the method. 



Of course a uniform application of the 

 same technique is not likely to prove 

 suitable for ever}' kind of material, but 

 the general principles are valid, requir- 

 ing a few modifications depending upon 

 the particular type of material. No 

 single method can be recommended 

 which would prove adequate for all 

 stages of development. The methods 

 that have proved particularly satisfac- 

 tory and have given the best results are 

 the Feulgen-smear-squash technique of 

 Coleman, L. C, Am. J. BoL., 1940, 27, 

 887-895; Coleman, L. C, Genetics, 

 1943, 2S, 2-8; Hillary, B.B., Bot. Gaz., 



1939, 101, 276-300; Hillary, B.B., Ibid, 



1940, 102, 225-235; Heitz, E., Ber. d. 

 biol. Ges., 1930,53, 870-878; Darlington, 

 C. D., and LaCour, L. F., The Handling 

 of Chromosomes, 1942. New York: 

 The Macmillan Company; and McClin- 

 tock, B., Stain Tech., 1929, 4, 53-56. 



In my experience of maldng prepara- 

 tions for the study of somatic and meio- 

 tic chromosomes, the method given in 

 the schedule here has proven most satis- 

 factory. It is e3.sentially a modifica- 

 tion of the technique developed by Dr. 

 Coleman and his associates of the Uni- 

 versity of Toronto and may be applied 

 to a wide variety of materials, both 

 plant and animal. The tissues are 

 fixed in Carnoy, one of the Navashin 

 modifications or Flemming-Heitz. One 



