64 PHYSIOLOGICAL MORPHOLOGY 



of the precise nature of all the different forms of proteid is impossible. 

 Indeed, the very names of nuclein, albumin. &c., are simply generic terms 

 for different groups of proteids. 



It is the changeable, inconstant, and manifold nature of proteid 

 substances, which renders them of great importance, and makes them 

 essential in the maintenance of life. The different varieties of proteid ' 

 have widely different physiological properties, for enzymes, poisonous 

 tox-albumins, and even chitin, found in the cell-walls of fungi, all belong 

 to this group. 



A number of proteids also take part in the formation of living 

 protoplasm, and indeed, it is possible that in every organism a specific form 

 of proteid of local or general distribution is always present, for there is 

 actual evidence to show that different parts of the cell are characterized by 

 special forms of this material. Thus, the chromatin of the nucleus contains 

 much nuclein, while the spindle-threads of the cytoplasm are different 

 in composition and contain but little nuclein. In dead reserve food 

 material, however, nuclein may also be present. A certain difference 

 always exists between reserve food material and organically assimilated 

 substance, for the fo d material becomes of use to the organism, and is 

 partly converted into building material, only after it has undergone certain 

 preparatory changes. 



Both macro- and micro-chemistry lead us to conclude that certain 

 differences exist between the proteids of different plants, and other facts 

 point to the same conclusion. Thus it is evident that thermophile bacteria, 

 which can develop at 74 C, and spores, which, even when moist, can 

 withstand a temperature of ico C. for half an hour, cannot possibly 

 contain any forms of proteid which coagulate at the relatively low 

 temperatures fatal to ordinary plants. 



Summary of the chemical properties. The mode of treatment applied to 

 proteids in text-books of chemistry is a good illustration of how little is known 

 concerning them. A fairly good account of the better-known proteid substances 

 is given in several text-books of physiological chemistry 2 , in which the important 

 phenomena of solution, crystallization, coagulation, digestion, &c., are dealt with. 

 Although in these treatises animal proteids are chiefly considered, still all the more 



1 [The term ' proteid ' is here used in a slightly broader sense than is usually customary. Thus, 

 strictly speaking, mucin and chitin are probably not true proteids.] 



2 Neumeister, Lehrbuch d. Physiol. Chemie, 1893, Bd. I; Hammarsten, ibid., 2. Aufl., iSy:;; 

 Bunge, ibid., 3. Anfl., 1895 ; Hoppe-Seyler, Handb. d. physiologisch-pathologisch chemischen Ana- 

 lyse, 6. Aufl., 1893. A full account of the vegetable proteids is given by Drechsel, under the heading 

 ' Eiweisskorper/ in the Handvvorterbuch d. Chemie, Bd. Ill, 1885; also by F. Schwarz, Cohn's 

 Beitrage z. Biologic, Bd. V, 1887. On the relations between animal and vegetable proteids see 

 E. Schulze, 'In wie weit stimmen Pflanzen u. Thierkorper in ihrer Zusammensetzung iibevein,' 

 Sep.-abdr. aus d. Vierteljahrsschrilt d. Naturf.-Ges. in Zurich, 1894 ; Palladia, Zeitschr. f. Biologic, 

 1894, p. 191 ; Fleurent, Compt. rend., 1893, T. cxvil, p. 790. 



