In the following experiments an attempt is made to measure the heat liberation of the ovum on fertilisation and early development, and to correlate this with the amount of oxygen consumed and the carbon dioxide given off at the same time. New methods hitherto unused for this purpose have been employed. The question has already been investigated by Meyerhof (1) in an extensive paper published in 1911. He determined the heat production and the oxygen consumption of the egg of the sea-urchin
Strongylocentrotus
on fertilisation and early development. The heat production was measured directly by means of a finely divided Beckmann thermometer, while the eggs were contained in a small closed vacuum flask completely submerged in the water of a carefully regulated thermostat. The oxygen consumption of the eggs was at the same time determined at intervals of an hour, by the titration of the sea-water in which the eggs were kept with sodium thiosulphate by the Winkler method. The heat given off by a known quantity of eggs expressed in gram claories per hour, divided by the amount of oxygen consumed in the same time expressed in milligrams, gave him a calorific quotient which he calls “Q.” This he found for the early stages of segmentation to be about 2.75, but if the heat of solution of carbon dioxide to form bicarbonate with the sea-water is taken into consideration this value becomes 2.6. This figure is so low, however, as to suggest that his data for the heat liberation or the oxygen consumption are incorrect, or that the oxidation processes of the egg-cell on fertilisation are of a different character from those of adult metabolism. It has been shown by Zunst and Schumberg, Rauber, Pflüger and others, that when fat is consumed this figure should be in the vicinity of 3.3, when protein 3.2, and carbohydrate 2.9. Meyerhof could find no carbohydrate in the egg, and there could be no destruction of protein, but sufficient fat was found in the egg to give the quotient observed. In the case of fresh sperm, Q was 3.1 or nearly normal. The carbon dioxide production by the eggs was not measured.