A modification of the Schmuck-Metz whole-mount technic for chromosome study.

Abstract

Chromosome study in small organisms has been discouraged by the difficulties involved in embedding and sectioning and in analysis of serial sections, as pointed out by Schmuck and Metz in 19128. These authors outlined a technic for making whole mounts of Sciara eggs and suggested that it might be applicable to other small objects. The author has modified this technic somewhat in accordance with recent suggestions of other investigators and has used it with success on Arhacia eggs. Chaetopterus eggs and larvae, small nematods, small insect eggs and embryos, and insect ovaries.' In all cases exceptionally good fixation and staining of chromatin were obtained. For example, in Chaetopterus larvae with a large number of cells, chromosome studies can be made of all cells in the process of division. Literally, hundreds of specimens can be fixed, stained, and ready for mounting with three hours of work, and large numbers can be mounted in a short time. METHOD Material is fixed in shell vials. If it settles readily, as is the case with marine eggs and larvae and small nematods, fluids are poured over it and subsequently removed with a pipette. Objects which tend to float, such as insect eggs, are wrapped in lens paper sacs. These are transferred from one fluid to another and are not opened until material is ready for mounting. Kahle's fixative (distilled water 30 ml., 95% alcohol 15 ml., formalin 6 ml., glacial acetic acid 1 ml.) is used and is excellent for invertebrate material in general. Fixation of insect eggs is improved if they are punctured. This is unnecessary for other objects studied. The stain is made by bubbling sulphur dioxide gas into 0.5% basic fuchsin solution until it is decolorized. The sulphurous acid bath is prepared by saturating distilled water with sulphur dioxide gas (Rafalko, 1946). Shell vials containing specimens in normal HCl are placed in a water bath at 'This study was carried on with the aid of a research grant from the National Cancer Institute of the National Institute of Health, U. S. Public Health Service.