34 II. FOOD RESERVES IN SITU. 



rim. If the tube be lowered, the black rim disappears, and the 

 disk shows a somewhat brighter contour. If the tube be raised, 

 the black rim becomes, on the other hand, broader. The oil- 

 drops' show, therefore, exactly opposite appearances to those 

 which we saw on p. 15 were exhibited by air-bubbles. Air is less 

 highly, oil more highly, refractive than water ; hence their oppo- 

 site relations ; and these relations should be carefully noted for 

 future use. 



If we run absolute alcohol under the cover-glass of the 

 \preparation of Eicinus which we have placed in water, the 

 preparation will " clear " somewhat ; and, simultaneously, the 

 protein crystals in the aleurone grains come out very sharply. 

 They are now so clearly defined that this method of manipulation 

 is recommended in order to study their form tetrahedral 

 hemihedra of the regular system. With longer action of the 

 alcohol, the oil-drops disappear more and more, as castor oil, in 

 contradistinction to other fat oils, is miscible with absolute 

 alcohol. 



Now make another preparation of Eicinus seed, lay it on the 



glass-slide in a drop of glacial acetic acid, and cover it with a 



cover-glass. The protein crystals swell quickly and disappear 



.in the aleurone grains ; these latter increase considerably in 



I volume, the globoids show up very clearly in each aleurone 



1 grain. Oil drops are, however, not visible, 'because castor oil, 



again an exception to the rule, mixes with glacial acetic acid. 



Apart from this case absolute alcohol and glacial acetic acid, 



because normally they either not at all or but slightly dissolve 



fat oils, while on the other hand they are solvents of ethereal 



oils, are the best reagents for the purpose of distinguishing 



between these two classes of oil under the microscope. Of 



ethereal oils, the terpenes dissolve somewhat less easily than the 



others in both the above reagents. Chloroform and ether dissolve 



fat and ethereal oils equally. To a preparation mounted in water 



run in alcannin tincture (alkanet root) diluted with water. The 



oil masses soon accumulate the colour and stain reddish-brown, 



. a reaction which ethereal oils and also resins alike show. 



Eeactions of Proteids. Aleurone grains of Eicinus and other 

 plants form excellent material for the study of the general 

 reactions of protein substances. Aleurone grains do not always 

 contain enclosures, as a comparison of Lupinus and Eicinus 

 (above) will show ; we can therefore distinguish the general body 



