66 PHYSIOLOGICAL MORPHOLOGY 



such as mucin, are formed. Nuclein may unite with albumin to form nucleo- 

 albumins, and to this class the plastin of microscopists probably belongs. In 

 nuclein, from 3 to 9-6 per cent, of phosphorus is present ; in nucleo-albumin, the 

 proportion is naturally lessened. Similarly, in glucosides the percentage of nitrogen 

 frequently diminishes from the 16 per cent, of typical albumin to as little as 

 10 per cent. 



Mucin, keratin, chitin, &c., are examples of albuminoids, and are substances 

 which, though obtained principally from animals, are also undoubtedly widely 

 distributed in the vegetable kingdom. 



The different forms of proteids, and their combinations and derivatives, are 

 used by the plant in various ways ; thus nuclein takes a very prominent part in the 

 formation of the nucleus, nucleo-albumins are often found in the form of food 

 material (legumin, conglutin, &c.), and the plastin of which the cytoplasm appears 

 to be very largely composed contains less phosphorus than nuclein does, and is 

 hence probably a nucleo-albumin '. 



Micro-chemical research indicates that the chromatin threads are composed 

 mainly of nucleins rich in phosphorus, and that the nuclear substance in which 

 these threads are embedded is composed of proteids, which are readily dissolved 

 by an acid solution of pepsin 2 . 



Nuclein is not digested by pepsin, and only with difficulty by trypsin, and hence 

 these very properties may possibly render it especially useful as a building material 

 or permanent skeletal framework. When nucleo-albumins are used as food material, 

 nuclein may either be obtained directly by the molecule being split into two, or the 

 living substance may itself form the nuclein building material, after the nucleo- 

 albumin food material has been assimilated by it. 



Both from a chemical and from a physiological point of view, it seems inad- 

 visable to give special names to characterize all the minute micro-chemical points of 

 difference which exist between the various forms of proteid ; for, as is well known, 

 micro-chemical properties may be markedly modified by infiltration with small 

 quantities of other substances. Hence it is only natural that the attempts by 

 F. Schwarz 3 to replace the general groupings of proteid substances by a series of 

 such special names have met with but little success 4 . 



The Changes which accompany Death. When the plasma is killed, it undergoes 

 a variety of chemical and physical changes, indicated by the loss of plasticity, by 

 the separating out of various mineral, proteid or pigment 5 substances, and by other 



1 Malfatti, Bot. Centralbl., 1893, Bd. LV, p. 152. See also F. Schwarz, Cohn's Beitrage, 1892, 

 Bel. v, p. 126. 



3 See Malfatti, Schwarz, &c., I.e., for the action of ferments on nuclein; Popoff, Zeitschr. f. 

 physiol. Chemie, 1894, Bd. xvm, p. 539. See also Zimmermann, Zellkem, 1896, and Zeitschr. f. 

 Mikroskopie, 1896, Bd. XII, p. 458. 



3 F. Schwarz, Cohn's Beitrage z. Biologic, 1892, Bd. v. 



4 See O. Hertwig, Zelle, 1893, p. 37; Zimmermann, Beihefte z. Bot. Centralbl., 1893, Bd. in, 

 p. 322. 



5 Pfeffer, Unters. a. d. Bot. Inst. z. Tubingen, 1886, Bd. II. p. 276. See also Campbell, ibid., 

 p. 569. 



