CHARACTERISTICS OF LIVING MATTER 7 



developing organism. The property of self-multiplica- 

 tion possessed by these units, on which the possibility 

 of their special action depends, is, however, not peculiar 

 to them, as already pointed out, but is a property of 

 protoplasm and of protoplasmic structures in general.^ 

 Once the chromosomes have been produced by this 

 autosynthetic process, they are free to exercise their 

 special influence and function. In this respect they 

 are like other structures which are definite factors in 

 the formative processes; they must first be synthesized 

 by the fundamental growth processes before they can 

 function. There are obvious analogies between the 

 action of the chromosomes and the action of special 

 form-determining chemical substances (or hormones) 

 produced by various organs. Development at certain 

 stages is demonstrably a consequence, as regards certain 

 special features, of the previous development of the 

 thyroid or the pituitary gland or the gonads. An even 

 more general analogy may be pointed out here, since 

 it illustrates the nature of many biological sequences. 

 A prerequisite to the normal activity of the adult is the 

 development of the normal adult structure; for example, 

 the formation of hands must precede the construction of 

 a house, but we do not explain the whole constructive 

 process by reference to the hands, the tools for sorting 

 and distributing the materials. How the chromosomes 

 influence formative metabolism is the essential problem 

 for physiology; this problem is at present unsolved, but 

 there can be no doubt as to the existence of this 

 influence. 



^H. J. Muller has discussed the properties of the genes from this 

 point of view in a recent paper in American Naturalist, LVI (1922), 32. 



