June 19, 1914] 



SCIENCE 



909 



kind is then required to continue deyelopment 

 despite the fact that the oxidations are going 

 on to their fullest extent. That it is their 

 fullest extent is indicated by the interesting 

 fact that even complete cytolysis of an egg 

 by saponin will not further accelerate its 

 rate of oxidation. 



Loeb analyzes the effect of the sperm in 

 initiating development into two factors — - 

 first, the sperm contains a lysin, not readily 

 diffusible into the egg of the same species, but 

 readily so into eggs of other species, which 

 produces a surface cytolysis. The surface 

 cytolysis leads to membrane formation in eggs 

 which form fertilization membranes as part 

 of their normal development. Foreign cells 

 and foreign fluids may contain similar 

 " lysins," but eggs are immune to lysins of 

 cells of the same species because they are 

 impermeable to them. Hence they must be 

 carried in by actual penetration of the sperma- 

 tozoon. In most eggs, especially sea urchins, 

 a second substance must also be carried into 

 the egg to prevent the destructive effect caused 

 by superficial cytolysis. Some eggs, Asterina, 

 Polynoe and Thalassema, do not require the 

 second corrective factor, due possibly to the 

 fact, as Loeb suggests, that they already con- 

 tain it or automatically form it. Again we 

 note variability in an apparently fundamental 

 point. The effect of the lysin is imitated by 

 the various membrane-forming substances 

 which if too concentrated lead to complete 

 cytolysis of the egg. The effect of the second 

 substance is imitated by the various correct- 

 ing agencies, hypertonic sea water, low tem- 

 perature or a prevention of oxidations by 

 KCN and chloral hydrate. 



The lysin, the membrane-forming substance, 

 is the essential in causing development. How 

 does it act? At present only suggestions can 

 be made. A possible method and a very simple 

 one would be the removal of some substance 

 which prevents development. This view which 

 has been suggested and discussed by Loeb and 

 other authors seems the most probable one 

 to-day. The problem of fertilization becomes 

 as much a question of what causes the egg cell 

 to cease development in a certain stage as of 



the cause for its further development by the 

 entrance of a spermatozoon. In physiological 

 terms we may say that the stoppage of devel- 

 opment appears to be due to an inhibiting 

 substance, that it is an auto-narcosis. The 

 lysin in the sperm or any artificial method 

 of causing development, even the prick of 

 a needle, allows the inhibiting substance, the 

 narcotic, to pass out. This result is possibly 

 obtained, although Loeb does not definitely 

 uphold this view, through increase in per- 

 meability of the ess. As already mentioned 

 oxidations are not diminished in the resting 

 condition of the starfish egg and it is inter- 

 esting to note, as shown by Loeb, that oxida- 

 tions in artificially narcotized cells are like- 

 wise not diminished. Narcosis is not due to 

 asphyxiation but is probably due to decreased 

 permeability. Certainly research along the 

 line of cell permeability, especially function- 

 ally conditioned changes in permeability is the 

 most promising field for a solution of the 

 problem of development, as of many other 

 biological processes. 



The reader interested in developmental 

 mechanics will be well repaid by a close 

 study of Loeb's book. Here is collected 

 in condensed and readable form the results 

 of many years' study together with conclu- 

 sions and ingenious hypotheses which stimu- 

 late to additional discoveries along these and 

 other lines. 



E. Newton Harvey 



Princeton, N. J. 



Rochy Mountain Flowers : An illustrated guide 

 for Plant-lovers and Plant-users: with 

 twenty-five plates in color, and twenty-two 

 plates in black and white. By Frederick 

 Edward Clements, Ph.D., Head of the 

 Department of Botany in the University of 

 Minnesota, and State Botanist; Director of 

 the Pikes Peak Alpine Laboratory, and 

 Edith Schwartz Clements, Ph.D., In- 

 structor in Botany in the University of 

 Minnesota and in the Pilces Peak Alpine 

 Laboratory. The H. W. Wilson Company, 

 White Plains, N. Y., and New York City, 

 1914. Octavo, 392 pp. ($3.00.) 



