THE D1OSMOT1C PROPERTIES OF THE CELL 95 



unable to absorb commercial aniline-blue or nigrosin even when placed 

 in relatively concentrated solutions. 



The colouration produced does not give any indication of the nature 

 of the compound formed within the cell, any more than the detection of 

 glucose or nitrates in the dead cell enables us to determine in what form 

 these substances were present in the living cell. Hence we have no 

 justification for supposing that soluble substances found in the dead cell, 

 such as glucose or nitrates, cannot diosmose through the plasma, or if an 

 absorption of these substances can be proved to occur, that they are 

 retained in the cell, because the plasma permits them to diffuse inwards 

 but not outwards. When substances presented to the cell are absorbed 

 only because they have undergone, as frequently happens, an extra-cellular 

 modification rendering them capable of diosmosis, it is only to these modified 

 products, and not to the original substances, that a capacity for absorption 

 can be ascribed. 



Such preparatory changes are easy to determine, and perhaps only 

 take place in immediate contact with the plasmatic membrane. In order 

 to investigate the diosmotic powers of a given substance, and to find out 

 whether it diosmoses directly without undergoing any preparatory modifica- 

 tion, it is usually advisable to determine whether, and to what extent, 

 exosmosis is possible ; for if polysaccharides or proteids, for example, 

 appear in the surrounding water, it is hardly possible that they can have 

 been formed by extracellular synthesis or condensation from other 

 exosmosing substances. As a matter of fact, very many substances may 

 exosmose from living cells, and this is especially the case in fungi and 

 bacteria, from which substances may be excreted which can only with 

 great difficulty diosmose through parchment, such as peptones, albuminous 

 substances, and enzymes, which are also probably proteid in nature '. 

 Puriewitsch has observed an exosmosis of albuminous substance from the 

 living endosperm of Zea Mais and Phoenix, and from tubers of the Dahlia, 

 &c., while he found that asparagin may be extracted by water from the 

 living cotyledons of Litpimts. Similarly, Hanstein and Puriewitsch 2 found 

 that an exosmosis of glucose was possible from the living endosperm of 



1 On the excretion of enzymes see Sect. 91. Albuminous substances and peptones are frequently 

 transferred from the living cells of fungi, bacteria, and yeast to the fluid in which they lie. It is, 

 however, important to remember that such transference also takes place when the cells die. \ or the 

 influence of external conditions on such excretion see Sect. 17. From the above, it maybe concluded 

 that albuminous substances and peptones may be absorbed by the living cell without undergoing any 

 previous change or decomposition. Certain organisms, having no power of producing proteolytic 

 enzymes, may be directly nourished with albuminous substances or peptone. See Beyerinck. 

 L' Aliment protogene, 1891, pp. 3 and 18 (Sep.-abdr. aus Archiv. Ne'erlandaises, T. XXIV) ; also 

 Sects. 66, 91, 108. 



2 Hanstein, Flora, 1894, Erg-.-bd., p. 419 ; Puriewitsch, Ber. d. Bot. Ges., 1896, p. 20'). See 

 Sects. 93, 109. 



