PRENATAL AND NEONATAL LUNG 211 



The fetal lung is opaque, and dense-looking, being often com- 

 pared in consistency with the thymus. Its color is dull gray- 

 ish-red. The breathing lung has a translucent pinkish color due 

 to the greatlj' increased flow of blood, and to the presence of 

 air. It floats upon water in contrast to the non-breathing lung, 

 and this is utilized as a medico-legal test. When the breathing 

 lung is moved between thumb and finger, the characteristic crepi- 

 tations are elicited. 



In sections the postnatal lung shows congested blood-vessels, 

 in striking contrast with the fetal lung, which shows but little 

 blood. It w^ould seem from examples of lung, which we obtained 

 from still-born animals, that the increased flow of blood begins im- 

 mediately, when the thoracic cavity is enlarged under the action of 

 the muscles. These examples were from kittens, which were born 

 at full-term. Tvvo of them were found with the fetal membranes 

 intact, and had never breathed air, while one of the litter had 

 breathed freely. In the lungs of the non-breathing animals, the 

 spaces were distended slightly more than in the normal fetal lung 

 and the blood-vessels were much congested. The animals had 

 evidently tried to begin to breathe air, but had only succeeded 

 in inspiring the liquor amnii. It would appear that, as soon as 

 the negative pressure commences, more of the blood stream is 

 deflected into the pulmonary arteries, less going through the 

 ductus arteriosus, and this occurs irrespective of what is being 

 drawn into the lung spaces. 



APPEARANCE OF LUNG OF PREMATURELY BORN ANIMAL 



An important factor in the expansion of the lung is the stage 

 of development of the fetus at birth, that is, whether it is pre- 

 maturely born or not. In a kitten born one week before the 

 remainder of the litter, we had an opportunity of seeing this 

 condition. This kitten had the appearance of a healthy normal 

 annual, although somewhat undersized. It crawled about and 

 cried vigorously w^hen disturbed but lived only about twelve hours. 

 Sections from the lung of this animal showed evidence of the 

 struggle to start and maintain respiration. The general appear- 

 ance is given in the outline drawing, figure 7. The bronchi are 



THE AMERICAN JOURNAL OP ANATOMY, VOL. 15, NO. 2 



