THE ORIGIN OF PLASM ATIC ORGANS 49 



these, like the living plasmatic organs visible to us, grow and increase, nourish 

 themselves, and reproduce their kind by division. All hypotheses put forward to 

 explain the phenomena of heredity involve an assumption of the existence of such 

 minute living elements ; while the same conclusion must also be drawn from 

 comparison and analogy with the perceptible structure of the living protoplast. 



The physiological units of Spencer, the gemmules or pangens of Darwin 

 (and also of de Vries), the idioplasmatic elements of Nageli, the plasomes of 

 Wiesner, the biophores of Weismann, are all ultimate units of living substance ', 

 but to give a detailed account of all the different hypotheses connected with 

 these terms is beyond the purpose of this text-book. Besides, the general 

 principles recognized as regulating the interactions between the parts visible 

 to us must also apply to the invisible physiological units, to which the general 

 term ' Pangen ' will here be applied. These are the primary living units, and 

 may be combined into units of higher ordinal value in a variety of ways, while 

 these again unite to form the organs and structural components of the protoplast. 

 These primary units could hardly all be precisely similar, but even if there were 

 only a few distinct types, still the number of possible combinations is illimitable. 

 A concrete example of similar character is afforded by the alphabet, the letters of 

 which can form a vast number of words, while an endless number of thoughts may 

 be expressed by the combination of these into sentences. In the host of carbon 

 compounds known to chemists we have a direct example of the number of com- 

 binations which can be made from three or four elements. With regard to the 

 protoplast, however, it is more probable that a large, or even a vast number 

 of pangens or physiological units, all differing from one another, enter into its 

 composition. 



Living substance is therefore to be regarded as being built up of pangens. 

 The changes and transformations which go on in the former may affect numerous 

 pangens or single ones only. In certain cases pangens, i. e. portions of the living 

 substance, may be used to form useful though non-living organs. 



A pangen would, in general, only be able to nourish itself, grow, and divide, 

 when combined with other pangens to form a unit of protoplasm. A pangen can 

 hardly be a micella, but must be built up of a number of micellae, or perhaps 

 molecules, arranged in a specific manner. Various chemical elements may thus 

 take part in the formation of a pangen, either directly combining to form it, or 

 forming part of the micellae of which it may be constructed. In the pangen, just as 

 in any machine, the manner in which the component parts are linked together is 

 all-important, and although qualitative or quantitative differences may possibly exist 

 between different pangens, these are not necessarily essential. A pangen must 

 resemble living substance in being capable of imbibition and swelling, while its 

 hypothetically complicated structure is in no wise antagonistic to the micellar theory 

 or hypothesis put forward to explain the nature of organized structures 2 . 



These few remarks must suffice, and in conclusion attention may be called to 



1 A complete account of the different theories is given by Delage, La structure du protoplasma 

 et 1'heredite, 1895. See also Wiesner, Elementarstruktur, 1892; Hertwig, Zelle, 1893, p. 267. 



2 See sect. 13; Pfeffer, Studien z. Energetik, 1892, p. 158. 



PFEFFER E 



