PRENATAL AND NEONATAL LUNG 207 



removing cellular debris, from the liquid-filled spaces. They also 

 resemble the 'heart-failure cells' of the lung which are seen in 

 certain pathological conditions. Several views are held as to the 

 nature of these phagocytic cells in the breathing lung, but the 

 study of these very similar appearing cells in the fetal lung, leads 

 one to agree with Kolliker ('02 vol. 3, p. 310), that they are a 

 form of 'Wanderzellen,' and not desquamated epithelium. 



NEONATAL LUNG ONE HOUR OLD 



When the respiratory muscles first begin to act at the begin- 

 ning of neonatal life, the thoracic cavity is enlarged. In con- 

 sequence of the relation between thorax and pleural sacs the 

 lung is likewise enlarged and inspiration is the result. With the 

 increase in size of the lungs to occupy a larger volume, the frame- 

 work of the organ is stretched and put on a tension, while the 

 spaces become larger. This is easily apparent when one com- 

 pares figures 4 and 3, showing the lung of a dog which had breathed 

 one hour, and a fetal lung respectively. By examining sections 

 across the entire lung and sections from different regions, it can 

 be seen that expansion does not take place equally in all parts 

 of the lung, nor in any particular area do all the alveoli and air- 

 sacs increase alike. As a result it was not easy to arri\'e at a 

 quantitative estimation of the area of lung-tissue and of the air- 

 passages, as seen in the sections. In regions, which had not been 

 much inflated, and did not appear much more open in character 

 than fetal lung, the framework still occupied 60 per cent of the 

 total area. But in regions where the respiratory channels were 

 more dilated, it occupied only 40 per cent or in restricted areas 

 even less. Thus there is a variation in the ratio, but in general 

 it may be said that the tissue occupies 40 to 60 per cent of the 

 area of the cross-section. The fact that the lung does not expand 

 at once after birth was seen also in newborn albino rats. These 

 were obtained from The Wistar Institute of Anatomy with the 

 aid of Dr. Stotsenburg. These young were taken immediately 

 after birth, before they were dry and before they had begun to 

 feed. Examination of their lung (fig. 6) shows that some areas 

 have been inflated very little, in contrast with other parts, which 

 are c^uite expanded. 



