152 L. V. HEILBRUNX. 



index is very close to that of sea-water. Now it is well known 

 that many proteins have a refractive index close to that of sea- 

 water; on the other hand, lipoids have a considerably higher 

 refractive index. As the refractive index is an additive function 

 of the constituents of a mixture, the presence of lipoids in any 

 abundance would make it impossible for the refractive index of 

 the membrane even to approach that of sea-water. Hence no 

 great admixture of lipoids can be present. More direct evidence 

 of the absence of any appreciable quantity of lipoids is also avail- 

 able. The membrane was tested with a Scharlach R solution 

 such as recommended by Herxheimer. In order to render them 

 more visible, the membranes were made to swell by placing the 

 eggs in 15 c.c. sea-water plus 10 c.c. 2.57VNaCl. To a drop of 

 Scharlach R solution on a slide was added a drop of egg suspen- 

 sion. The vitelline membrane remained hyaline and unstained, 

 whereas the egg cytoplasm itself was colored red. The Scharlach 

 R solution used in this test was a saturated solution of the dye 

 in equal parts of acetone and 70 per cent, alcohol. 



If the egg contents be made to flow out from the membrane or 

 if the egg be cut or shaken into fragments, a new membrane 

 immediately forms around the momentarily naked protoplasm. 1 

 Such a membrane has the same chemical properties as the vitel- 

 line membrane. The acids and salts which produce swelling 

 in the latter, cause it to swell also. The immediate production 

 of a protein membrane about these egg fragments must be re- 

 garded as similar to the formation of precipitation membranes 

 like those studied by Traube and Quincke. Evidently, some 

 protein contained in the egg is precipitated on contact with the 

 outer sea-water. It is probable that this protein is, in the in- 

 terior of the egg, prevented from coagulation by the presence of 

 a protecting colloid. At the outer surface of the egg, the mem- 

 brane-protein is coagulated by direct contact with sea- water. 

 Support for this view is found in the fact that the presence of 

 some colloids (e. g., egg albumen) in the sea-water, causes the 

 membrane to take up water and swell. Since the vitelline mem- 



1 O. and R. Hertwig in their " Untersuchungen zur Morphologic und Physiologic 

 der Zelle," Heft 5, 1887, first observed the elevation of membranes on egg frag- 

 ments. (This observation was also repeated by Ziegler, Arch. f. Ent. Mech., VI., 

 249 (1898), by Moore, Univ. of California Publications in Physiology, IV., 89 (1912). 



