FATTY METAMORPHOSIS OF PULMONARY EPITHELIUM. 387 



layer which, in a puerperal corpus luteum, is of very 

 great breadth and has a rather reddish yellow tint ; in a 

 menstrual corpus luteum it is narrower, and very dis- 

 tinctly separated on the inner side from the freshly ex- 

 travasated contents which have filled up the follicle emp- 

 tied by the extrusion of the ovule. This internal red 

 mass- consists entirely of thrombus, or blood-clot. The 

 external layer essentially consists of fattily degenerated 

 cells, and the yellow colour which it bears is occasioned 

 by the refraction produced by the numerous minute par- 

 ticles of fat. This is not a real colour, but a phenome- 

 non of interference. 



A similar change you see in a lung which we took to- 

 day out of the body of a man who, after caries of the in- 

 ternal ear, had a thrombosis of the transverse sinus with 

 gangrenous metamorphosis, and, in consequence, gan- 

 grene of the lung. The cells we have here to deal with 

 were not taken, however, from the actual seat of the gan- 

 grene itself, but from a condensed spot in the neighbour- 

 hood, where a very abundant accumulation of masses of 

 proliferating epithelium (catarrhal pneumonia) had taken 

 place. In this case you can see the difference between 

 fat- granule -cells (Fig. 66), and other forms of granule- 

 cells, very prettily shown. For in these masses of epi- 

 thelium which have filled up the alveoli of the lung, you 

 find extremely numerous pigment-cells, such as in cases 

 like this are brought up in great quantity in the sputa, 

 which are indebted to them for the well-known smoky 

 grey spots (Fig. 11, b). A& first sight it is difficult to 

 make a distinction between fat-granule-, and pigment- 

 cells, inasmuch as in both cases apparently the same 

 image is offered to our view. In the one case the cells 

 appear as brownish yellow corpuscles, although their indi- 

 vidual particles have no positive colour ; in the other, on 

 the contrary, they contain unquestionable, grey, brown, 



