QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by MITCHISON, J. M. Articles by SWANN, M. M. Search for Related Content PubMed Articles by MITCHISON, J. M. Articles by SWANN, M. M.

Journal of Experimental Biology 31,461-472 (1954)
Published by Company of Biologists 1954

The Mechanical Properties of the cell Surface : II. The Unfertilized Sea-Urchin Egg

J. M. MITCHISON ¹ and M. M. SWANN ¹

¹ The Department of Zoology, University of Edinburgh; the Marine Station, Millport; and the Stazione Zoologica, Naples

1. Measurements were made with the cell elastimeter on the stiffness of the cell membrane in the unfertilized eggs of five species of sea urchin. Young's modulus varies in the different species between the values of 0.91 x 10⁴ and 2.08 x 10⁴ dynes/cm².

2. Experiments on the change of stiffness in hypo- and hypertonic media indicated that there is probably no internal pressure and no membrane tension in the normal egg. If, however, there is an internal pressure, measurements of the minimum shrinkage of the membrane necessary to produce wrinkling showed that this pressure cannot exceed 95 dynes/cm².

3. A drop in temperature of 18.5° C. produced an increase of stiffness by a factor of 2.1.

4. These experiments, together with other evidence, suggest that for mechanical purposes the unfertilized sea-urchin egg can be compared to a hollow sphere filled with fluid and surrounded by a solid elastic wall (the membrane or cortex) about 1.5 µ thick and with an elastic modulus about 1-2 x 10⁴ dynes/cm². This degree of rigidity is sufficient to ensure the maintenance of shape of the egg without the presence of an internal pressure or a tension in the membrane. In everyday terms, the egg therefore resembles a tennis ball or a child's rubber ball, rather than an inflated balloon or an oil drop in water.