File:Contributions from the Botanical Laboratory, vol. 11 (1934) (20500298058).jpg

Title: Contributions from the Botanical Laboratory, vol. 11
Identifier: contributionsfro11univ (find matches)
Year: 1934 (1930s)
Authors: University of Pennsylvania. Botanical Laboratory; University of Pennsylvania. Morris Arboretum
Subjects: Botany; Botany
Publisher: Philadelphia : (s. n. )
Contributing Library: Penn State University
Digitizing Sponsor: Lyrasis Members and Sloan Foundation

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
416 THE SCIENCE OF RADIOLOGY THE GURWITSCH RAYS 417 Among the Russian workers, other than Gurwitsch, Baron (2), and Frank (6, 7, 8) stand first. The chief contribution of the former is the discovery that yeast is an efficient sender and receptor of the vital rays. Baron succeeded in obtaining a sufficiently great increase in the growth of yeast cultures to be distinguished with the naked eye. Proof is, therefore, macroscopic as well as microscopic. The area of the treated culture is visibly larger than that of the control (the controls run very uniform), and the number of cells per unit area in the field when microscopically viewed, is considerably greater in the treated cultures. Baron made the addi- tional discovery that the yeast cultures must be used at a definite time in their life cycle. Salkind (47) has likewise demonstrated a rhythmic nature in the emanation from developing sea-urchin eggs, and Gurwitsch has stated that yeast cultures, after being transferred, must run for 12 to 15 hours at 25-28°C. for successful radiation. Twenty hours is too long. Only cultures which double or triple in cell number in four hours are suitable as detectors. More sluggish, or more active cultures do not respond. The situation is similar with the fruit-fly, Drosophila, which when used as a source of Gurwitsch rays must be taken at a definite time in its life cycle, namely, just before and during pupation of the lar- vae. Such facts as these, when unknown, become pitfalls for less experienced workers. Later work has revealed what is rather a general rule in biologic processes, namely, that frequent, successive, short exposures are more effective than one long continuous exposure. Intermittent exposure of yeast cultures to a ray source from which they are separated by a re- yolving, notched (fractioning) disc, increases the effect so that the time of ex- posure has been lowered in some cases to twenty seconds (16). The earlier method for ascertaining J- . . 1 , , , r whether or not acceleration of cell division had resulted from induction was the laborious one of counting the cells which show mitotic (dividing) figures (in onion tissue), buddW (t yeast) or an increase in cell number (in bacteria). This method has, in the case of yeast and bacteria, been replaced by a very neat technic. For yeast the
Text Appearing After Image:
Fig. 104.—The centrifuge-capillary test: left treated, right control. (From Gurwitsch.) f/) ' i4) procedure is as follows: the cells are radiated in open tubes or chambers, then 0.2 cc. of the radiated and the control cultures are accurately pipetted off into small test tubes which contain 1 cc. of fresh sterile beer-wort. The cultures are put into an oven at 25-28°C. for three or four hours, then killed with sulphuric acid and thoroughly shaken. Fine capillary ("Myzetokrit" or hematocrit) tubes are filled, one containing the treated and one the control culture. The capillaries are then centrifuged, precipitating the yeast cells which pile up in the bottom and reveal the results of the experiment in a graphic manner (fig. 104). Bacterial cultures present a more difficult problem because of the minute- ness of the organisms. The following method, which may also be used for

Note About Images