The Organism as a Whole, from a Physicochemical Viewpoint

by Jacques Loeb

By this method fifty per cent. or more of the eggs of purpuratus could be fertilized with the sperm of the starfish Asterias ochracea, capitata, Ophiurians, and Holothurians, while with the sperm of another starfish, Pycnopodia spuria, only five per cent., and with the sperm of Asterina only one per cent. could be fertilized.[60] Godlewski succeeded by the same method in fertilizing the eggs of a Naples starfish with the sperm of a crinoid.[61] The writer did not succeed in bringing about the fertiliza­tion of the egg of another sea urchin in California, Strongylo­centrotus franciscanus, with the sperm of a starfish. Although these eggs formed a membrane in contact with the sperm, the latter did not enter the egg; nor has the writer as yet succeeded in causing the sperm of Asterias to enter the egg of Arbacia.

Kupelwieser[62] observed that the spermato­zoön of molluscs may occasionally enter into the egg of S. pur­pur­atus in normal sea water and later, at Naples, he observed the same for the sperm of annelids. In these cases no development took place. In teleost fishes the spermato­zoön can enter the eggs of widely different species but with rare excep­tions all the embryos will die in an early stage of development.[63]

2. The fact that an increase in the alkalinity or in the concentra­tion of calcium allowed foreign sperm to enter the egg of the sea urchin, suggested the idea that a diminu­tion of alkalinity or calcium in the sea water might block the entrance of the sperm of sea urchin into eggs of their own species. This was found to be correct; when we put eggs and sperm of the same species of sea urchin into solu­tions whose concentra­tion of Ca or of OH is too small, the sperm, although it may be intensely active, cannot enter the egg.

For the purpose of these experi­ments the ovaries and testes of the sea urchins were not put into sea water, but instead into pure m/2 NaCl and after several washings in this solu­tion were kept in it (they remain alive for several days in pure m/2 NaCl). Several drops of such sperm and one drop of eggs were in one series of experi­ments put into 2.5 c.c. of a neutral mixture of m/2 NaCl and ³⁄₈ m MgCl₂ in the propor­tion in which these two salts exist in the sea water. In such a neutral solu­tion eggs of Arbacia or purpuratus are not fertilized no matter how long they remain in it, although the spermatozoa swim around the eggs very actively. That no spermato­zoön enters the eggs can be shown by the fact that the eggs do not divide (although they can segment in such a solu­tion if previously fertilized in sea water or some other efficient solu­tion). When, however, eggs and sperm are put into 2.5 c.c. of the same solu­tion of NaCl+MgCl₂, containing in addi­tion one drop of a N/100 solu­tion of NaOH (or NH₃ or benzylamine or butylamine) or eight drops of m/100 NaHCO₃, most, and often practically all of the eggs at once form fertiliza­tion membranes and segment at the proper time, indicating that fertiliza­tion has been accomplished. The same result can be obtained if the eggs are transferred into a neutral mixture of NaCl+MgCl₂+CaCl₂ (in the propor­tion in which these salts exist in the sea water) or into a neutral mixture of NaCl+MgCl₂+KCl+CaCl₂. In such neutral mixtures the eggs form fertiliza­tion membranes and begin to segment. The eggs are not fertilized in a neutral solu­tion of NaCl or of NaCl+KCl.[64]

It is, therefore, obvious that if we diminish the alkalinity of the solu­tion surrounding the egg and deprive this solu­tion of CaCl₂ we establish the same block to the entrance of the spermato­zoön of Arbacia into the egg of the same species as exists in normal sea water for the entrance of the sperm of the starfish into the egg of purpuratus.

The “block” created in this way, to the entrance of the sperm of Arbacia into the egg of the same species is also rapidly reversible.

We reach the conclusion, therefore, that the specificity which allows the sperm to enter an egg is a surface effect which can be increased or diminished by an increase or diminu­tion in the concentra­tion of OH as well as of Ca. The writer has shown that an increase in the concentra­tion of both substances may cause an agglutina­tion of the spermatozoa of starfish to the jelly which surrounds the egg of purpuratus.[65] It is thus not impossible that the specificity which favours the entrance of a spermato­zoön into an egg of its own species may consist in an agglutina­­tion between spermato­zoön and egg protoplasm (or its fertiliza­tion cone); and that this agglutina­tion is favoured if the C_OH or C_Ca or both are increased within certain limits.

Godlewski discovered a very interesting form of block to the entrance of the spermato­zoön into the egg which takes place if two different types of sperm are mixed. He had found that the sperm of the annelid Chætopterus is able to enter the egg of the sea urchin and that in so doing it causes membrane forma­tion. The egg, however, does not develop but dies rapidly, as is the case when we induce artificial membrane forma­tion, as we shall see in the next chapter.

Godlewski found that if the sperm of Chætopterus and the sperm of sea urchins are mixed the mixture is not able to induce development or membrane forma­tion, since now neither spermato­zoön can enter; blood has the same inhibiting effect as the foreign sperm. The mixture does not interfere with the development of the eggs if they are previously fertilized.[66]

The phenomenon was further investigated by Herlant[67] who found that if the sperm of a sea urchin is mixed with the sperm of certain annelids (Chætopterus) or molluscs, and if after some time the eggs of the sea urchin are added to the mixture of the two kinds of sperm no egg is fertilized. If, however, the solu­tion is subsequently diluted with sea water or if the egg that was in this mixture is washed in sea water, the same sperm mixture in which the egg previously remained unfertilized will now fertilize the egg. From these and similar observa­tions Herlant draws the conclusion that the block existed at the surface of the egg, inasmuch as a reac­tion product of the two types of sperm is formed after some time which alters the surface of the egg and thereby prevents the sperm from entering. This view is supported not only by all the experi­ments but also by the observa­tion of the writer that foreign sperm or blood is able to cause a real agglutina­tion after some time if mixed with the sperm of a sea urchin or a starfish.[68] We can imagine that the precipitate forms a film around the egg and acts as a block for the agglutina­tion between egg and spermato­zoön. The block can be removed mechanically by washing.