Preface to the Fourth Edition 



BIOLOGY has advanced very rapidly during 

 the past eight years. Thus it is difficult merely 

 to list the new material that has been incor- 

 porated into this fourth edition of Principles 

 of Modern Biology. However, some main 

 topics that have been added or brought 

 thoroughly up-to-date may be specified as 

 follows: (1) Electron microscopy: fine struc- 

 ture of the endoplasmic reticulum; centrioles; 

 plastids; grana; mitochondria; muscle fila- 

 ments; cilia; flagella; the plasma membrane; 

 synaptic membranes; chromosomes; the mi- 

 totic apparatus; pinocytic vacuoles; ribo- 

 somes; etc. (2) Cellular metabolism: isotope 

 tracer and chromatographic methods; the car- 

 bon path in photosynthesis; photochemical 

 phenomena, especially photophosphoryla- 

 tion; thermodynamics of intracellular energy 

 transactions; role of ATP; electron transport 

 systems; the Krebs cycle; glycolysis and fer- 

 mentation; theory of enzyme action; activa- 

 tion energies; enzyme-coenzyme interactions 

 and amino acid activation. (3) Protein struc- 

 ture: methods of determining the amino acid 

 sequence of the primary structure and the 

 role of hydrogen bonds and other linkages in 

 determining secondary and tertiary structure. 

 (4) DNA-RNA-protein interrelationships: 

 the Watson-Crick model; mechanisms of self- 

 templated replication; the base-pair rule in 

 DNA-RNA synthesis; the genetic code; mes- 

 senger and transport RNA, (5) Genetics: 

 population analysis, abnormal chromosome 

 complexes in relation to heritable "errors of 

 metabolism." (6) Nature of the gene: analysis 

 of the base sequence in viral replication and 

 in cell-free bacterial preparations; cis-trans 



phenomena; gene-enzyme interrelationships; 

 enzyme induction; morphogenesis and dif- 

 ferentiation; basic nature of mutational 

 changes. (7) Ecology: the ecosystem concept; 

 producers, consumers, and decomposers; 

 abiotic base; ecological succession; pioneering 

 and climax stages. (8) New phytohormones 

 and photoperiodism. (9) Antibody produc- 

 tion in relation to the thymus gland. (10) En- 

 docrine advances: the parathyroid hormone; 

 erythropoiten; the pineal hormones; neuro- 

 humors generally; cellular and comparative 

 endocrinology; feedback mechanisms; ho- 

 meostasis in general. (11) Receptors: chem- 

 istry of vision; generator potentials; excita- 

 tory substances. (12) Effectors: newer con- 

 cepts of muscle structure and function; chem- 

 istry of luminescence. (13) Central nervous 

 system: fine structure of the synapse; neuro- 

 secretory vesicles; integrative functions of 

 neurons; transmitter substances; pacemaker 

 and other types of potential. (14) Excretory 

 system: concept of homeostasis; evolution of 

 the vertebrate kidney. Many other more 

 specific data of recent origin have been inter- 

 polated at appropriate points in the various 

 chapters of the book. 



Considerable attention has been given to 

 the illustrations. Many new photographs, 

 particularly electronmicrographs, have been 

 added and there are quite a few new draw- 

 ings. A number of the old drawings have been 

 relabeled for the sake of greater clarity, and 

 special attention has been paid to the cap- 

 tions. The purpose in this connection has 

 been to provide each figure with an inde- 

 pendent interest without sacrificing the pri- 



