rHYSloLOmCAL I'HEXO.MKXA IX THE FlETI's. \2% 



which constitute a gradually increasing proportion of the corpuscular 

 components of the blood during the latter period of embryonic life, or 

 whether these are formed only by the metamorphosis of lymph-cor- 

 puscles, has not yet been determined. 



From the manner in whicli the circulation is carried on during firtal 

 life, and which has been adverted to, it is seen that the chief propelUng. 

 power is centred in the right side of the heart ; the force of tlie left 

 heart being mainly spent in elYecting a due supply of blood to the head 

 and upper extremities. And the structure of the heart proves this to 

 be the case, for the walls of the right ventricle have been found as 

 thick as those of the left ; while the walls of the right auricle are even 

 thicker and more muscular than those of the left auricle — a condition 

 which persists for a short time after birth. 



The isolation that exists in the two circulatory systems might lead 

 to the inference that there was no relation between the contractions of 

 the heart in the foetus and those of the maternal organ, and experience 

 proves this to be the case. Naegele has noted that there is no relation 

 between the beats of the heart of the human fa^tus and those of its- 

 mother's heart. By auscultation he was able to distinguish the two 

 sounds of the fcjetal heart, and found it beat on an average 135 times 

 per minute — never more than 180, nor less than 90 ; and he remarked 

 that the beats were sensibly the same from four and a half months, when 

 they are first perceptible, until birth. And Hollmann, in resorting to 

 the same mode of investigation in Cows, ascertained that, in one which 

 was advanced eight and a half months in pregnancy, and whose pulse 

 was G4 per minute, the foetal beat was l^l ; in another Cow, but which 

 was ill, the pulse was from 70 to 112, while that of the foetus was 113 

 to 128. 



Colin opened a living Mare which had been pregnant for )iine or ten 

 months, and a Cow whose gestation dated about three months. When 

 the uterus of the Mare was opened, and the contained envelopes incised 

 to extract the fa3tus, the latter moved actively and respired deeply, 

 though at rare intervals. The umbilical arteries and vein yielded some 

 blood, from the small punctures made through their walls ; the lirst 

 throbbed with a certain amount of force, and the pulsations were rapid. 

 When the cord was divided and tied, the foetus appeared to be dead : 

 there were no more spontaneous movements, and the respiration had 

 ceased. The thorax and the abdomen were now thrown open, and it 

 was observed that the heart contracted spontaneously and strongly, and 

 the pulsations of the aorta and umbilical arteries could be very distinctly 

 felt. At first the contractions of the auricles regularly alternated with 

 those of the ventricles, as in a normal condition ; but soon, as occurs in 

 expiring animals, the auricles contracted several times fur one contrac- 

 tion of the ventricles, as if it required several systoles of these to fill the 

 ventricular cavities. At each contraction the auricles diminished nmch 

 in volume, became nearly empty, and looked very pale, but assumed 

 their reddish-violet colour again during their diastole. At last tlie 

 rhythmical movements became altogether perverted ; the auricles and 

 ventricles contracted simultaneously and quickly, but more and more 

 feebly, and finally ceased altogether half an hour after the thorax had 

 been opened. The Cow in which the foetal circulation was studied had 

 its flank widely incised, and one of the cornua of the uterus withdrawn 

 through the opening. Some of the placentula) were removed with 

 difliculty from their cotyledons, and both bled a good deal When the 



