728 THE RESPIRATION AND [pt. iii 



rate was four times as small as that of the adult. The same conclusions 

 applied to carbon dioxide. 



These investigations led to a long-continued discussion in which 

 a dichotomy of opinion soon presented itself Pfliiger, who had 

 always affirmed that the metabolic rate of embry^os was far smaller 

 than that of fully grown animals, welcomed Cohnstein & Zuntz's 

 work as a confirmation of his views. The embryo, he said, has need 

 for practically no muscular movement, and lives in a liquid of 

 specific gravity very like itself, so there can be no necessity for great 

 expenditure of energy, and therefore no " bemerkenswerthe Respira- 

 tion". Gusserov took another view. Abstracting Pfluger's papers for 

 the Archiv f. Gyndkologie in 1872 he said that, although it might be 

 true that muscular motion was at a minimum in embryonic life, yet 

 the astonishing rapidity of growth might equally well demand a 

 considerable expenditure of energy. "You cannot overlook", he re- 

 marked, "the amazing speed with which the embryo passes from the 

 tiniest size to the weight of the foetus at term, and this phenomenon 

 can hardly take place without an active metabolism." Gusserov's 

 words contain the origin of the notion of "Entwicklungsarbeit", 

 afterwards so much elaborated by Tangl. But, although all those who 

 took part in the controversy admitted that experiments alone could test 

 the matter, none were carried out until 1900, when Bohr took it up 

 anew. Cohnstein & Zuntz's second paper was only concerned 

 with the arterial pressure before and after birth, the causes of foetal 

 apnoea, and the first stimulus for pulmonary respiration at birth. 



Bohr attacked the problem again with the advantage of improved 

 methods, and he showed that the majority of the errors imperfectly 

 guarded against by Cohnstein & Zuntz would act in the direction 

 of making the metabolic rate too low. He abandoned the direct 

 method used by them of estimating the blood-gases in the umbilical 

 cord, and instead measured the oxygen consumption and carbon 

 dioxide production of the maternal organism (guinea-pig) before, 

 during, and after, clamping of the umbilical cord, i.e. cutting out 

 altogether the influence of the embryo. In a typical experiment after 

 compression of the umbilical cord the carbon dioxide excretion fell 

 by 10 c.c, and the oxygen utilisation by 11 c.c, per 10 minutes. 

 When the clamp was taken off the respiration at once rose to its 

 former value, and fell again to just the same extent towards the end 

 of the experiment when a ligature was put on the umbilical cord. 

 In 10 minutes, therefore, the embryo gave out 10-5 c.c. carbon 



