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CHARLES
Ε.
WILDE
and exchange between the protoplasm and non-protoplasmic compartments takes place is well established. So also there is evidence for
exchange between protoplasms and between adjacent micro-environments. The number of possibilities at this level is in itself bewildering.
Historically, it has proven difficult to find the words to make intellectually precise concepts of this nature.
The protoplasmic compartment can be morphologically divided into
nucleus and cytoplasm. This is obviously an unsatisfactory division
since interactions between the two occur. However, there is heuristic
value in the division because it serves to place differential emphasis
upon the known properties of each.
The nucleus is the seat of synthesis of DNA and its attached proteins.
DNA is considered to be the source of heritable synthesis and to be the
form in which heritable biochemical characteristics are transferred from
cell to cell and from organism to organism. Genetics and its modern
biochemical analysis have produced concepts which have made theoretical order out of the means of heredity. DNA is concentrated, particularly at cell division, in morphological entities, the chromosomes, whose
duplication and equal partition into daughter cells has led to the firmly
held opinion that each cell in an animal contains ab initio an equal and
complete set of heredity transfer cues or genes. Evidence for differential
segregation of this material, while available in certain forms, has not
been sufficient to overturn the 'complete set' hypothesis (Stern, 1958).
Now polymerized DNA or DNP has sufficient native variability to
account for the large but finite numbers of hereditary determiners
estimated from formal genetic studies. Also biochemical genetics has
developed cogent concepts of means whereby genes act in synthesis of
protein enzymes which are the indubitable agents required for synthesis
and for protoplasmic energetics. The details of order and the clarity of
the analyses in biochemical genetics have of themselves led to great difficulties in the analysis of cellular differentiative processes (Ephrussi,
1956,1958). The apparent absence of genetic (DNA synthetic) differentials
between cells of differing form and functions coupled with the apparent
biochemical differences between cells of differing type have led to great
difficulties in the design of rational hypotheses concerning the means of
cellular differentiation. It should, however, be immediately stated that
evidence is now being brought forward to the effect that nuclear
differentials do exist between cells. In the larvae of Díptera, Beerman
(1952), and Breuer and Pavan (1956), have adduced data of the temporal differential appearance of characteristic 'puffs' or Balbiani rings
at specific chromosomal loci in specifically differentiating areas of the
embryo. King and Briggs (1956; Briggs and King 1957), from their
nucleus transplantation studies, have brought forward evidence that in
CHARLES
Ε.
WILDE
and exchange between the protoplasm and non-protoplasmic compartments takes place is well established. So also there is evidence for
exchange between protoplasms and between adjacent micro-environments. The number of possibilities at this level is in itself bewildering.
Historically, it has proven difficult to find the words to make intellectually precise concepts of this nature.
The protoplasmic compartment can be morphologically divided into
nucleus and cytoplasm. This is obviously an unsatisfactory division
since interactions between the two occur. However, there is heuristic
value in the division because it serves to place differential emphasis
upon the known properties of each.
The nucleus is the seat of synthesis of DNA and its attached proteins.
DNA is considered to be the source of heritable synthesis and to be the
form in which heritable biochemical characteristics are transferred from
cell to cell and from organism to organism. Genetics and its modern
biochemical analysis have produced concepts which have made theoretical order out of the means of heredity. DNA is concentrated, particularly at cell division, in morphological entities, the chromosomes, whose
duplication and equal partition into daughter cells has led to the firmly
held opinion that each cell in an animal contains ab initio an equal and
complete set of heredity transfer cues or genes. Evidence for differential
segregation of this material, while available in certain forms, has not
been sufficient to overturn the 'complete set' hypothesis (Stern, 1958).
Now polymerized DNA or DNP has sufficient native variability to
account for the large but finite numbers of hereditary determiners
estimated from formal genetic studies. Also biochemical genetics has
developed cogent concepts of means whereby genes act in synthesis of
protein enzymes which are the indubitable agents required for synthesis
and for protoplasmic energetics. The details of order and the clarity of
the analyses in biochemical genetics have of themselves led to great difficulties in the analysis of cellular differentiative processes (Ephrussi,
1956,1958). The apparent absence of genetic (DNA synthetic) differentials
between cells of differing form and functions coupled with the apparent
biochemical differences between cells of differing type have led to great
difficulties in the design of rational hypotheses concerning the means of
cellular differentiation. It should, however, be immediately stated that
evidence is now being brought forward to the effect that nuclear
differentials do exist between cells. In the larvae of Díptera, Beerman
(1952), and Breuer and Pavan (1956), have adduced data of the temporal differential appearance of characteristic 'puffs' or Balbiani rings
at specific chromosomal loci in specifically differentiating areas of the
embryo. King and Briggs (1956; Briggs and King 1957), from their
nucleus transplantation studies, have brought forward evidence that in