Studies on the Hydrogen-Ion Concentration of Insect Blood and Their Bearing on in vitro Cytological Technique

Abstract

I N DISPUTES over the visible structure of cytological objects it is customary to refer, if possible, to what can be seen in the or normal cell. This sort of evidence has long been used, for example, in investigations on mitochondria, Golgi bodies, and spindle fibers; and recently it has been appealed to in studies on the perplexing structure of the giant salivary gland chromosomes of dipteran larvae. In the last instance, however, the reports based on material agree no better than those from fixed preparations. Thus Bauer (1935) and Painter and Griffin (1937) maintained that chromosomes were visible in salivary gland nuclei of Chironomus and Simulium, respectively, whereas Doyle and Metz (I935a, b) and Caspersson (1936) maintained that they were not visible in Sciara and Drosophila, respectively. Since several species were used in these investigations, the-reported differences might represent interspecific variation. This idea is supported, in part, by the observations of Buck (1939) in which Chironomus, Drosophila, Sciara, and Simulium were studied by an in vivo technique, which obviated the need for dissection and its consequent possibilities of injury and were found to differ in the visibility of their chromosomes. On the other hand, Barigozzi (1938) worked on the same species as Bauer (Chironomus Thummi) and reported that the chromosomes were sometimes visible and sometimes not. This indicates either a locality difference, as suggested by Barigozzi, or a difference in the techniques used to examine the chromosomes. The usual method for in vitro study of normal or giant chromosomes has been to excise the salivary glands and examine them either in a salt solution of more or less arbitrary composition or in the body fluid (blood or haemolymph) of the larva, either with or without a covering of paraffin oil.2 Similar methods are adequate for some material, particularly where cell division or growth can be used as a criterion of normality. This has been amply demonstrated, for example, by the studies of Chambers (1925) and Bel~ar (1929) on living grasshopper spermatocytes and by tissue-culture work.3 Nevertheless, the discordant reports cited earlier (and others) indicate strongly that in vitro methods have been inadequate, as applied to giant chromosomes.