THE RESPIRATORY SYSTEM 163 
pulmonary substance, thought to originate in the alveolar 
epithelium and occasionally gromng to large size; the 
case in the kangaroo may have had this origin. It tvas 
the only primary tumor to give metastasis (to the spleen 
and gastric wall), the secondaries being decidedly ade- 
nomatous in character. 
Metastatic growths come from the following originals : 
two from the thyroid, well Imown to give pulmonary 
embolism in dogs; one each from the breast, uterus, 
adrenal, intestine and kidney. The form assumed is a 
gray and red mass lying under the pleura or an isolated 
nodule in the substance. Sarcomatosis, the form appar- 
ently spreading out from the hilum and growing in 
isolated grayish tubercular masses, has not been seen. 
The Pleura. 
The pleura is a tissue apparently quite susceptible to 
infection in mammals and so closely associated with the 
air sacs in birds as to be a part of the same membrane, 
therefore the two being affected together. Throughout 
the higher class all orders give copious examples of the 
involvement of the pleura, principally of course as an 
accompaniment or a sequel to pneumonitic or bronchitic 
processes but also as a part of acute infectious diseases, 
such as hemorrhagic septicemia, pleuropneumonia and 
the like. However two orders present such a number of 
instances of pleuritis that they deserve notice. The seals, 
Piniiipedia, of which we have twenty autopsy records, 
showed inflammation of this membrane four times, three 
of wliich were dependent upon pulmonary infection and 
one apparently due to general septicemia with trifling 
damage to the lung proper. One of the first cases had 
gone on to empyema of the classical type, a shrivelled dry 
almost carnified lung with a thick fibrinopurulent cover- 
ing. The lung of the seal is well divided into lobules, the 
external surface being generously supplied with lym- 
phatic channels under the pleura, an arrangement which 
