REVIEWS. 89 



meshes corresponding to the superficial alveoli of the lung, 

 which in early stages are filled with cells which are 

 undoubtedly altered epithelium ; and later, by cells indistin- 

 guishable from lymphoid cells. These nodules are to the 

 naked eye at first rounded, grey, and transparent ; later they 

 increase in size, become of a more irregular shape, and their 

 centre becomes opaque and caseous. This central softening 

 extends gradually in all directions to the circumference, and 

 the nodule which first forms a distinct prominence on the 

 pleural surface, becomes depressed in the centre when soften- 

 ing is advanced. 



In the substance of the lung Dr. Klein distinguishes 

 granulations of three kinds. (1.) More or less well-defined 

 nodules in connection with the walls of small bronchi. 

 These he regards as simply hyperplasae ofthe normal adenoid 

 tissue of this part. They are found at a comparatively late 

 stage and do not soften. (2.) Perivascular cords. These 

 are developed earlier around the small arteries, at first as 

 endolymphangeal follicles by plugging of lymphatics with 

 lymphoid cells, and their subsequent conversion into cords of 

 adenoid tissue, and then the cords become further thickened 

 by a perilymphangeal growth. Changes also take place in the 

 blood vessels themselves. The endothelium of the ultimate 

 branches of the pulmonary artery is found to germinate so 

 as very materially to diminish the lumen of the vessel. In 

 larger branches the middle coat becomes laminated, and infil- 

 trated by lymphoid cells which extend into the coats of the 

 vesselfrom the perivascular cords; finally the capillary vessels 

 in the alveolar walls become ultimately converted into 

 nucleated threads. This change takes place only in the later 

 stages of the process, subsequent to a thickening of the 

 alveolar septa by encroachment of the perivascular cords. In 

 the perivascular cords no caseous degeneration (softening) 

 was ever found. (3.) The last kind of granulations is due 

 to catarrhal pneumonia. The alveolar septa become thickened 

 as above described, and the alveoli themselves become blocked 

 at first by alveolar epithelial cells and their derivatives, giant- 

 cells forming a prominent feature. The largest of these 

 Dr. Klein believes to originate from a fusion of several 

 epithelial cells, as their substance shows an indication of 

 being divided into territories. The catarrhal changes finally 

 spread from the alveoli to the infundibula and small bronchi. 

 It is these catarrhal pneumonic granulations which undergo 

 caseation, a process which spreads at last to the thickened 

 alveolar septa. 



The last chapter is devoted by Dr. Klein to an account of 



