Adaptive Growth

of a symposium. In the present one, chapters are well-organized, opposing or complementary views of the same subject are conveniently juxtaposed, the sometimes amorphous discussion at the end of a group of papers is summarized succinctly rather than printed verbatim, and there is a useful index and bibliography of references. Dr. Franklin McLean has written a helpful introduction containing a summary of progress in the field since 1960. Although the book is a convenient collation of good current papers on the parathyroid, it is not an all-inclusive review; for example, there is no discussion of methods of measuring parathyroid hormone in plasma, as by radio-immunoassay. Perhaps the most exciting news in this area in the last 10 years is the discovery by Dr. Harold Copp of a factor secreted by the dog's parathyroid which lowers serum calcium (calcitonin). A calcium lowering hormone has also been isolated from the thyroid (thyrocalcitonin). These are discussed in papers by Copp and by McIntyre. Lawrence Raisz has an excellent discussion of the regulation of the manufacture and release of classical parathyroid hormone, derived from experiments using parathyroid glands cultured in vitro. In these cells Ca++ has a direct effect on aminoacid uptake and hormone release, probably through its effect on the outer cell membrane. There are several papers on the histological changes produced by parathyroid hormone as well as the biochemical alterations responsible for reabsorption of bone. These are good examples of the application of standard modern techniques to bone tissue but one gets the impression that the answer to the question, "Why does parathyroid hormone dissolve bone?" is still elusive. The fact that isolated mitochondria take up calcium from the surrounding medium has attracted much interest, especially since under some circumstances the trapped calcium can be released when parathyroid hormone is added. Two papers in the symposium deal with this phenomenon. It is not clear, however, that this is related to the physiological action of either of the two parathyroid hormones. The parathyroids influence the transport of phosphate by the kidney as well as the gut, and experiments elucidating this action are discussed by W. F. Neuman. This volume is an interesting summary of current published research on the parathyroids that will be useful to laboratory workers and clinical scientists. FRANKLIN H . EPSTEIN