388 LECTURE XVI. 



or black, pigment. The diagnosis of ordinary granule- 

 cells, by which fat-granule-cells are always meant, is, 

 however, very important, because in other parts also, as 

 for example, in the brain, we find both sorts of granule- 

 cells, those containing fat and those containing pigment, 

 side by side ; and even when the affection is limited to 

 very small spots in this organ, it is very important* for 

 the interpretation of the objects found to know whether 

 they belong to the one or the other class. For in the 

 brain also the accumulation of a number of minute par- 

 ticles of fat may on the whole, through the multiplication 

 of the refracting points, occasion an intense yellow colour. 

 The different proportion of fat and the degree of its divi- 

 sion produce a greater number of varieties of colour which 

 at last manifest themselves very distinctly to the naked 

 eye, so that the more minute and the more closely ag- 

 gregated the fatty particles are, the more marked is the 

 production of a pure yellow or brownish-yellow hue even 

 to the naked eye. What we call yellow softening of the 

 brain is also really nothing more than a form of fatty de- 

 generation, where the yellow appearance of the affected 

 spot is owing to the accumulation of finely granular fat. 

 As soon as this is removed, the colour also disappears, 

 although the fat thus extracted is by no means of so deep 

 a hue as the spot whence it was derived. The refraction 

 of light between the extremely minute particles is the 

 chief cause of this phenomenon of colour. 



It is self-evident that at every point, where the fatty 

 degeneration attains a high pitch, great opacity will 

 always present itself. A transparent part becomes 

 opaque when it undergoes fatty degeneration ; this we 

 see, for example, in the cornea, the fatty clouding of 

 which may become so marked in arcus senilis, that an en- 



* Eor the pigment would point to apoplexy, the fat to softening. 



