82 



PROXIMATE PRINCIPLES OF THE SECOND CLASS. 



STARCH GRAINS FROM WALT, OP LATERAL 

 VENTRICLES; from a woman aged 35. 



really substances of a starchy nature ; since they exhibit the usual 

 chemical reactions of vegetable starch. 



The starch granules of the human brain (Fig. 6) are transparent 



and colorless, like those from 

 plants. They refract the light 

 strongly, and vary in size 

 from 4^0(7 to TT V^ of an 

 inch. Their average is ygViy 

 of an inch. They are some- 

 times rounded or oval, and 

 sometimes angular in shape. 

 They resemble considerably 

 in appearance the starch, 

 granules of Indian corn. The 



\ ^ / largest of them present a 



very faint concentric lamina- 

 tion, but the greater number 

 are destitute of any such 

 appearance. They have 

 nearly always a distinct hilus, which is sometimes circular and 

 sometimes slit-shaped. They are also often marked with delicate 

 radiating lines and shadows. On the addition of iodine, they become 

 colored, first purple, afterward of a deep blue. They are less firm 

 in consistency than vegetable starch grains, and can be more readily 

 disintegrated by pressing or rubbing them upon the glass. 



Starch, derived from all these different sources, has, so far as 

 known, the same chemical composition, and may be recognized by 

 the same tests. It is insoluble in cold water, but in boiling water 

 its granules first swell, become gelatinous and opaline, then fuse 

 with eachxDther, and finally liquefy altogether, provided a sufficient 

 quantity of water be present. After that, they cannot be made to 

 resume their original form, but on cooling and drying merely solidify 

 into a homogeneous mass or paste, more or less consistent, accord- 

 ing to the quantity of water which remains in union with it. The 

 starch is then said to be amorphous or " hydrated." By this process 

 it is not essentially altered in its chemical properties, but only in 

 its physical condition. Whether in granules, or in solution, or in 

 an amorphous and hydrated state, it strikes a deep blue color on 

 the addition of free iodine. 



Starch may be converted into sugar by three different methods. 

 First, by boiling with a dilute acid. If starch be boiled with dilute 



