122 LECTURE VII. 



tives, decomposing the substance, and by other means, we arrive at the 

 constitution of the body in question. We consider that the constitution 

 of a substance is definitely settled only when, by synthesis, we succeed 

 in reproducing the same substance. We must attempt to follow this 

 same line of procedure in our investigations with the albumins. We now 

 turn to the question of crystallizing the albuminous bodies. Crystals of 

 albumins have been known for a long time. T. Hartig, in 1850, 1 

 noticed crystalline substances in gluten meal, which are called aleuron grains 

 "protein granules/' or "plant crystalloids." The albuminous nature of 

 these crystals was established by Radlkofer. 2 They have been observed 

 in many seeds; for instance, in pumpkin seeds, hemp seeds, ricinus 

 seeds, and especially in the Brazil nut. A beautiful example of this 

 kind of crystallization is presented by parasitical plants of the order 

 Orobanchacece, the tooth- wort, 3 Lathrcea squamaria. The cell kernels con- 

 tain protein crystals. A vigorous discussion has arisen as to whether these 

 substances are real crystals, or whether they only possess a crystalline 

 appearance. They possess characteristics which do not correspond with 

 those of true crystals. In the first place, these crystalline-appearing 

 substances swell up under the influence of water, and also of dilute 

 alkali. The refractive index of the crystal then diminishes. The 

 crystalline form also changes, because it does not expand uniformly 

 along its various axes. They are also partially soluble in glycerin. 

 A solid homogeneous residue remains, which retains the form of the original 

 crystal. There has been much discussion about this phenomenon. Fr. 

 N. Schulz 4 has indicated an interesting analogous example of an inorganic 

 crystalline formation. If human urine is allowed to stand for 24-48 

 hours with dicalcium phosphate, and then filtered, a precipitate of crys- 

 tals, one-half mm. in size, appears when the liquid is allowed to evap- 

 orate of itself. The crystals are like honestone with ragged points, and 

 they are strongly refractive (in polarized light, doubly refractive). If 

 these crystals are treated with dilute acetic acid a part is dissolved. 

 A crystal remains, however, which has the form of the original. It is 

 now singly refractive towards polarized light, and has lost its former 

 high refractive index. The dissolved portion is calcium phosphate; the 

 remainder, calcium sulphate. It is possible that the protein crystals 

 mentioned possess analogous characteristics. There is, however, nothing 

 further known at present to warrant these substances being classed 



1 T. Hartig: Bot. Zeit. 50, 881 (1850). 



2 L. Radlkofer: Ueber Kristalle proteinartiger Korper pflanzlichen und tierischen 

 Ursp rungs, W. Engelmann, Leipzig, 1859. 



3 A. F. W. Schimper: Diss. Strassburg, 1878; Z. Kristal. 1880. F. N. Schulz: Die 

 Kristallisation von Eiweissstoffen u. ihre. Bedeutung f. d. Eiweisschemie, G. Fischer, 

 Jena, 1901. 



4 Fr. N. Schulz: loc. cit., p. 4. 



