748 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the determination of which it is appropriate, we shall examine the 

 different substances, and for each one point out the microchemical 

 operations which belong to it. 



IV. Precipitation, Crystallization. 



The substances whose precipitation or crystallization is produced 

 in the interior of the cells are asparagin, inulin, and the saccharoses. 

 Their deposition can be incited by a solution which contains principles 

 different from those that are being sought for or even (according to 

 the method originated by Borodin *) saturated with the substance 

 itself which it is proposed to discover. 



Asparagin. — Asparagin crystallizes in this way in cells when 

 treated with a saturated solution of asparagin. It is even the best 

 meaus of showing its presence. It is obtained in greater quantity by 

 immersing the tissues in absolute alcohol, which on subsequent 

 evaporation leaves the asparagin in crystals. But as the alcohol 

 also takes up other substances capable of crystallizing, in order to 

 recognize it, we treat all the crystals with a concentrated solution of 

 asparagin, in which this substance alone remains crystallized. 



It should be observed that the tissue in which it is to be studied 

 ought to be in active life, since asparagin, which is an acid of 

 bimalate of ammonia, constitutes a product of secretion, as it were 

 the urea of plants. 



Inulin. — Solid inulin can be obtained in the cells in two different 

 conditions ; in the amorphous or the crystalline. Desiccation causes 

 the precipitation of this substance, which previously existed dissolved 

 in the cell-sap ; it is most frequently amorphous. Nevertheless, when 

 desiccation is very slow, it crystallizes. 



Prolonged maceration of the organs which contain the reserve- 

 materials in alcohol causes the formation of sphero-crystals of inulin. 

 When sections are made of the tissue thus prepared, a little acetic 

 acid is added, and they are put in glycerin. 



The alcohol used must be diluted with water. It is advantageous 

 to reduce imperceptibly, by evaporation, the quantity of water added 

 to the alcohol, and to keep up the level of the liquid in the vessel by 

 adding to it gradually absolute alcohol. 



When there is not time to allow the organs to remain in the 

 alcohol before making sections, the sections themselves can be sub- 

 jected to the action of either absolute alcohol or ether. In this case 

 a deposit of amorphous inulin is obtained. 



Saccharose. — The saccharoses are insoluble in absolute alcohol. It 

 is therefore sufficient to treat the saccharine cells by this agent in order 

 to produce the crystallization of the saccharose. Bonnier "j" has often 

 had recourse to this process in the examination he has made of the 

 nectaries. By way of verification, he treated the soluble portion of 

 the tissue with 80 per cent, alcohol and with ether ; he then saw 

 crystals of the same form appear in the liquid. 



* Bot. Ztg., 1878, p. 804. 



t " Les Nectaires," Ann. Sci. Nat., 1870. Sec tliis Journal, ii. (1879) p. 7'18. 



