RESEARCH
marily for graduate student thesis work and postdoctoral research in t h e departments of chemistry and physics. Graduate students in other fields will also have access to bombardments and isotopes as time permits. The radiochemical studies to b e undertaken include such problems as fast neutron cross-section measurements by radioactivation techniques; investigation of decay scheme of short-lived nuclides produced by ( n , p ) , ( n , 2 n ) , (n,a), ( n , y ) , and similar reactions; and the study of chemical states formed in nuclear reactions.
How Does a Hydra Grow? Chemical principlesof g r o w t h can b e studied with a simple mode! system, the hydra H ow DOES a fertilized egg cell divide, and differentiate to form an embryo with the right number of t h e right kinds of cells in t h e right places? N o one knows, »but Richard G. H a m and Robert E. Eakin at the University of Texas think they have developed methods for using a simple model system that may help discover some of the basic chemical principles involved. Their model: the hydra, a primitive animal t h a t can regenerate lost parts rapidly. In many systems commonly studied—embryo of a chick, for example—many processes occur at once; so many, these workers say, that it is almost impossible to studyany one separately. In contrast, the regenerating hydra replaces only the few simple tissues which have been removed. As a lab tool, the hydra possesses other advantages also: • It reproduces asexually at a very rapid rate, providing a large colony of genetically identical animals maintained under identical conditions. • It is large enough (about one fourth inch long) to be handled easily individually, yet small enough so that large numbers can be worked with. • How a n d in W h a t O r d e r .
The
primary approach of t h e Texas researchers is to study the effect of biologically active chemicals on regeneration. T h e tentacle-bearing head is cut from the hydra and regeneration of new tentacles is observed after 18 hours. (This means each day's experiments can take into acount the previous day's results.) 26
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So far, the researchers have found a number of chemicals that inhibit regeneration—colchicine, amino acid analogs, purine and pyrrolidine analogs, nerve depressants, lithium salts, and 6substituted purines, among others. While no compound tested so far stimulates regeneration, some cause the animals to regenerate more tentacles than were originally removed—lithium chloride, for example; the pyrirnidine analog, 5-bromouracil, in contrast, sharply reduces the number. By using various inhibitors at various times during the regeneration period, Ham and Eakin are also getting some idea of the order of the events in regeneration. From these studies, they sketch a tentative picture of how regeneration proceeds: Almost immediately after the hydra are cut, a short burst of mitosis occurs, lasting less than an hour. After this regeneration is apparently primarily by cell migrations. Amino acid antagonists are active only very early; purines and pyrimidines are needed throughout most of the regenerative period. Nerve activity, judged by sensitivity to nerve depressants, is essential only in the later portion of the regenerative period. ALo, the number of tentacles regenerated can be lowered only very early; treatment at a later time is best for raising the number. From their data, the investigators postulate that primordia for the new tentacles are differentiated within the first four hours after cutting, and that, once established, they block any further primordia formation unless special measures are taken. Thus the investigators feel that the key to understanding the controlling mechanism of regeneration lies in these first four hours. Ham feels that biochemists have too often looked on living organisms as specialized test tubes within which to study certain types of chemical reactions or else as a source of crude materials for studies of composition. "These provide valuable background information," he says, "but it is time that the organisms are viewed not as mere containers but rather as complex chemical entities whose every life process has a chemical basis." While their work has only scratched the surface, the Texas scientists hope it may someday help show how cells develop normally and how they escape normal regulation to grow without control—cancer.
Actinides at Paris Europe works at extracting protactinium; O R N L extracts neptunium and americium on a n intermediate scale X HE ACTINIDE ELEMENTS
^ isolated
but one, got a big play at the XVTth International Congress of Pure and Applied Chemistry, held in Paris from July 18 to 24. Glenn T. Seaborg of the University of California, Berkeley, pointed out than when element 103 is discovered (C&EN, July 22, page 15) the actinide series will be complete. This series corresponds in the periodic table to the rare earth series beginning with lanthanum—the lanthanides. In both series as the number of electrons in the atom of each element in the series increases the electrons are added to an inner shell, rather than to the outer ones. Chemical properties, therefore, are roughly the same for all members of the series. When elements 104, 105, and 106 are discovered, they will fall under hafnium, tantalum, and tungsten in the periodic table. Their chemical properties should therefore be different from those of the actinides. Chemical properties of these "trans 1 0 3 " elements can be predicted for elements all the way up to 118. However, these higher elements wall be increasingly unstable with very short half-lives, and it is unlikely that anyone will ever see the higher members of this group. Seaborg points out that considerably more work is being done in Europe than in the U. S. on the extraction of protactinium, one of the naturally occurring actinides. Protactinium is about as plentiful in nature as radium and since it is an element, it deserves study. A. G. Goble, A. G. Maddock, and others at Cambridge University in England have extracted more than half a gram of protactinium from uranium refinery residues. Differential acid leaches were followed by precipitation by aluminum, a cyclic solvent extraction with HC1 solutions containing fluorides complexed by aluminum, and a re-extraction into aqueous fluorides. At the Institut du Radium in Paris, M. Lederer has been able to separate protactinium from a number of other elements by paper chromatography.
