6i6 THE RESPIRATION AND [pt. iii 



absence of the air. It is most interesting to note that none of these 

 early workers seemed to find any difficulty in the notion of a non- 

 pulmonary non-circulatory respiration. In 1840 Bucknell com- 

 mented on the increase in size of the air-space during incubation. 



Most of the attention given to embryonic respiration during the 

 earlier half of the last century was centred on the bird's egg, but a 

 few experiments were done on other eggs. In 1846 the Academy of 

 Sciences in Paris offered a prize for a memoir in which the candidates 

 were required to "determine by the aid of precise experiments what 

 is the succession of chemical, physical, and organic changes which 

 take place in the egg during the course of the development of the 

 foetus in birds and batrachians". The prize was won by Baudrimont 

 & Martin de St Ange, who produced a work which must be regarded 

 as one of the classics of chemical embryology. I shall refer later 

 to their general results on the metabolic changes which they in- 

 vestigated; it is only necessary to note here that they proved that 

 carbon dioxide was given off throughout incubation by the developing 

 eggs of hens, garden snails, lizards, snakes and frogs. They also 

 measured the daily loss in weight of developing hen's eggs, and did 

 not fail to note that this could be at least doubled by incubating 

 the eggs in an atmosphere which had been dried by sulphuric acid. 

 On the other hand, they affirmed that nitrogen was lost by the eggs, 

 and that an egg weighing 50 gm. would give off 0-055 S"^- of sulphur 

 in 21 days, presumably in the form of hydrogen sulphide. They 

 tried incubating eggs in oxygen, hydrogen and carbon dioxide, 

 observing in each case the teratological results, and analysing the 

 gases in the air-space. Frog's eggs placed in a vacuum were found 

 not to have developed at all. Other points investigated by these 

 workers were the permeability of the frog's egg to strychnine and 

 to morphine. But, for the present purpose, it is only to be noted 

 that they initiated the quantitative work on embryonic respiration. 



Curious experiments were also made at about the same time by 

 Rusconi and by Preyer, in which larval amphibia were raised in 

 the absence of atmospheric air, simply by the dissolved oxygen in 

 the circulating water, but they are not now of importance. More 

 interesting was the gasometric work of Bischof and of Dulk, who in 

 1823 and 1830 respectively, without knowing of Coxe's work, analysed 

 the gas which could be extracted from the whole egg when placed in 

 deaerated water in a vacuum. They both found it to have a higher 



