PRENATAL AND NEONATAL LUNG 203 



In order to secure histological material for a study of the 

 normal appearance of these lungs, another fetus of approximately 

 the same size was injected through the umbilical vein with 10 

 per cent formalin. Later the thorax was opened and after the 

 relations of the lung were observed, pieces of the lung were taken 

 for histological sections. The appearance as evidenced by char- 

 acters to be described later, was that of a lung which had not 

 made premature respiratory movements. 



The second series of experiments were repetitions of the fore- 

 going, performed on a litter of living dog fetuses lying within 

 the uterine horns of the mother. The parent animal was anes- 

 thetized and the young carefully exposed one at a time without 

 unnecessary manipulation. In order to prevent the entrance of 

 amniotic fluid, due to premature respiratory movements, the 

 trachea of each fetus used was clamped with an artery forceps 

 as soon as it was exposed and before the amnion was ruptured. 

 As a result of this stimulation the animal at once began to make 

 violent efforts to breathe, but if the trachea was well clamped 

 these were ineffectual and the animal soon died of asphyxiation. 

 The lungs were removed as described for the sheep fetuses, and 

 experiments carried out in a parallel way. The results were 

 similar to those of the first series, so it may be concluded that 

 normally in the fetal trachea, bronchi and lungs there exists a 

 liquid which resembles the amniotic fluid in appearance. The 

 question arises as to what becomes of this liquid when breathing 

 begins. From obser\'ations on fetuses removed from the uterus, 

 the first act in l^reathing is always inspiration. As the lung 

 enlarges, due to the contraction of the diaphragm and other re- 

 spiratory muscles part of the liquid in the upper parts of the tract 

 is drawn downwards and part remains distributed along the walls 

 of the air-passages. When the fetus inspires amniotic fluid before 

 its removal from the sac, it is always much handicapped. It 

 does not breathe so strongly, and its efforts become weaker, and 

 farther apart until they cease altogether. If in these circum- 

 stances, as we tried with young dogs, the animal be held with 

 head downwards, and the thorax compressed at short intervals, 

 the difficulty in l^reathing is often relieved, and the animal im- 



