726 THE RESPIRATION AND [pt. m 



4-15. Respiration of Mammalian Embryos 



The data which we have on the subject of the respiration and 

 heat-production of the mammahan embryo are very scanty and 

 fragmentary. The question has been handled usefully from an ob- 

 stetrical point of view by Harding; Murlin; and Feldman, but a 

 great deal of the information contained in their reviews lies outside 

 the scope of the present book, for it is concerned with changes in 

 the maternal organs during pregnancy. The modern period was 

 opened by Zweifel's discovery in 1876 that oxyhaemoglobin was to 

 be found in the umbilical blood of an infant that had never entered 

 on the pulmonary stage of respiration. This stimulated N. Zuntz to 

 try some experiments in which he asphyxiated the pregnant animal. 

 Most of the work was done by the simple method of ascertaining 

 whether the blood in given blood-vessels was arterial or venous, light 

 or dark, and in this way he found that on asphyxia the foetal circula- 

 tion would give up oxygen to the placenta and so to the vessels of 

 the uterine wall. Pfliiger himself added some remarks to Zuntz's 

 paper, and the line of investigation was continued some years later 

 by Cohnstein & Zuntz in collaboration. Their paper, which was very 

 long, was concerned to a large extent with measurements of blood- 

 volume, enumeration of blood corpuscles, etc., which need only be 

 mentioned briefly here. They were the first to discover that in the 

 earher stages of development the number of red blood corpuscles in 

 the foetal blood is very low, in certain cases only i or 2 being present 

 for every 10 in the maternal blood. A curve constructed from the 

 data of Cohnstein & Zuntz for the growth in the number of erythro- 

 cytes is shown in Fig. 440 (Section 17-1). 



They also made a good many experiments on the blood-count of 

 newly born infants, and gave in their paper all the literature on that 

 subject before 1884. The early work of Quinquaud; Convert; Wiske- 

 mann; and Hoesslin had not succeeded in providing any data on the 

 growth of the haemoglobin-content of the foetal blood, so Cohnstein 

 & Zuntz turned their attention to that, and obtained some inter- 

 esting results. Discussion of these, however, will be deferred to the 

 section on pigments. Cohnstein & Zuntz also measured the blood- 

 volume in rabbit embryos, and their findings are graphically repro- 

 duced in Fig. 161. The volume (expressed as per cent, of the embryo) 

 of the blood in the embryo rises; that of the blood in the placenta 



