Page:Popular Science Monthly Volume 86.djvu/575

Rh to hold the same view. E. N. Harvey, though believing that the membrane is not present before fertilization, considers the jelly unnecessary for its formation, holding that the membrane substance hardens on contact with sea water. He admits that unfertilized eggs from which the jelly is removed soon lose their power of forming membranes on fertilization, but says they do not lose it immediately. Perhaps he left a thin film of jelly adhering to the eggs or had not removed the water containing the dissolved jelly. This dissolved jelly may be in time decomposed by bacteria and thus prevent membrane formation. If eggs with jelly remain in sea water fifty-two hours, they do not form membranes on fertilization.

When a sea urchin's egg is fertilized, an increase in the rate of respiration occurs, as shown by O. Warburg. This may be due to some physical change, and is to be expected, since the egg passes from a state of inactivity to one of activity. When the starfish egg is liberated from the body of the female into the sea, it becomes active to the extent of extruding the polar bodies. Loeb and Wasteneys found that respiration was high at the time of formation of the polar bodies in the starfish egg, and continued about the same level, whether fertilized or not. The egg may pass through an inactive stage while in the ovary, with corresponding low respiration. Coming in contact with sea water may stimulate it toward development, with resulting maturation and increased respiration, though the stimulus is not sufficient to cause segmentation. This is in harmony with the fact that much weaker stimuli cause segmentation in starfish than are required by sea urchin eggs. The frog's egg resembles the former and Batallion has shown that the slight prick of a needle is sufficient to cause the frog's egg to segment, while needles have been thrust by the writer all the way through sea urchin's eggs without causing either segmentation or death.

O. Warburg has shown that the respiration of all developing eggs is high, regardless of the methods used to cause segmentation. Respiration is therefore essential to development. Cleavage once started may be slowed or stopped entirely without materially decreasing respiration, indicating that respiration is not a result of cleavage. In order to discuss the relation of respiration to development, it is necessary to go more into detail on the general question of respiration.

As is well known, the heat of a flame is unnecessary for the burning (oxidation) of many substances. For example, coal oxidizes slowly in the air, decreasing in weight, a fact which has led to efforts to preserve its fuel value by keeping it under water. Naturally, even slow combustion generates heat, and if the heat be confined, results in spontaneous combustion, i. e., the raising of the temperature to the flame point.