254 PHYSIOLOGY OF NUTRITION. 



0'2 per cent. Hydrochloric acid). Examination shows that the 

 protoplasm contracts, while the nuclei in the cells rapidly become 

 perfectly homogeneous. The nuclei then increase in volume, and 

 ultimately appear as yellowish, highly refringent structures, 

 which undergo no further change. When the nuclei, after be- 

 coming homogeneous, begin to increase in size, the contracted 

 protoplasm at one or more points swells out into a vesicle. 

 Finally this bursts, and now there are left only insignificant proto- 

 plasmic residues surrounding* the nucleus. Dilute Hydrochloric 

 acid does not alter nuclei treated with the artificial digestive 

 fluid, while they immediately dissolve in dilute soda solution. 1 



1 See Zacharias, Botan. Zeitung, 1881, p. 169. 



98. Microscopic Tests for Asparagin. 



I have energetically endeavoured to establish the view 1 that the 

 living proteid molecules of the protoplasm, the physiological ele- 

 ments as I term them, under all circumstances, and in every cell 

 in a state of vital activity, break down by dissociation into nitro- 

 genous and non-nitrogenous compounds (dissociation hypothesis). 

 These last are broken down in respiration, and provide the 

 material necessary for the growth of the cells, etc., while the 

 former soon accumulate in greater or less quantities in the cells, 

 or unite with non-nitrogenous substances 

 to reform proteids. Moreover, the nitre* 

 (J genous products of dissociation of the 



A physiological elements of the protoplasm 



FIG. 92. - Asparagin (asparagin, glutamin, leucin, tyrosin, allan- 

 crystais. (After Zimmer- toin)' are of great significance, inasmuch as 

 they play an important part in the trans- 

 location of substances in the plant. 



Of all the nitrogenous decomposition products of proteids, 

 aspara^in (amidosuccinamic acid) appears to be of the greatest 

 importance. For this reason we shall give it particular atten- 

 tion, and firstly learn how to detect its presence in plant-cells 

 microchemically. 



Asparagin is almost completely insoluble in alcohol, and there- 

 fore if we treat a concentrated aqueous solution of it with absolute 

 alcohol, the asparagin separates out. Similarly by means of 

 alcohol we can precipitate asparagin occurring in solution in the 



