MOLECULAR STRUCTURE OF ORGANISED BODIES. 35 



the direction of greatest swelling is at right angles to the 

 indications of structure : thus, in a starch-grain or in a cell- 

 wall, the direction of greatest swelling is at right angles to the 

 layers of stratification. 



Before leaving this part of the subject it will be well to 

 say a few words concerning the proteid crystalloids which 

 have been already mentioned more than once. These are 

 true crystals which differ from other crystals only in that they 

 are capable of swelling-up. They are usually considered 

 to be organised bodies, but it appears from the researches 

 of Van Tieghem on the Mucorini that they are not formed 

 by the organising activity of living protoplasm, but by simple 

 crystallisation, and Schimper has shewn that their swelling-up 

 is regulated by the same laws which govern the expansion of 

 other crystals when heated. 



We will now turn to Strasburger's explanation of the 

 optical properties of organised bodies. He points out that, 

 on the micellar theory, organised structures such as cell-walls 

 and starch-grains should not lose their optical properties 

 when their organisation is destroyed, for the particles of the 

 disintegrated micellae would, like particles of broken crystals, 

 still retain their double refraction, and they would there- 

 fore also continue to exert a depolarising effect. But this 

 is not the case. Organised structures cease to be doubly 

 refractive at the moment when their organisation is destroyed. 

 Naegeli himself states that when starch-grains and cell-walls are 

 made to swell excessively by treatment with acids or alkalies, 

 or by heating, they soon completely lose their double refraction. 



It appears, then, that the optical properties of organised 

 structures are dependent upon their organisation. They may 

 be chemically altered by treatment with reagents, their form 

 may be changed by physical forces, but their optical properties 

 remain, provided that their organisation is not affected. Stras- 

 burger's account of the nature of this organisation is to the 

 following effect. Cell-walls and starch-grains consist of suc- 

 cessive lamellae which are in different states of tension and 

 are firmly adherent ; and just as a piece of glass becomes 

 doubly refractive when differences of tension are set up within 



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