42 THE QUANTITATIVE METHOD IN BIOLOGY 



produced by the coexistence of two or more factors — that, for 

 instance, a certain factor C is able to produce a property a as 

 often as a certain factor A is also present, and another property 

 h when it meets a certain factor B, but that neither C nor A 

 nor B are able to produce any observable property when they 

 are isolated.^ 



A factor is a hypothetical something which is to be found in 

 the hving mixture. It may be surmised that a factor corre- 

 sponds to a certain bioprotein, or to a certain abiotic substance 

 (enzym, chromogen, etc.) ^ produced hy the living mixture. 

 Although it is impossible to reach the actual bottom of the 

 problem because of our ignorance of the chemical composi- 

 tion of the living mixture, I think that the theory of the 

 hereditary factors may be further developed by a more 

 complete investigation of the primordia in a series of species ^ 

 according to the method expounded in the present work. 

 (See Part IX.) 



Whatever it may be, by means of the ingenious but rather 

 complicated theory of the hereditary factors ^ it has already 

 been possible to classify and to explain numerous facts which 

 seemed to be capricious and inscrutable. 



It may be remarked once more that this very important part 

 of natural science is based upon the use of the quantitative 

 method initiated by MENDEL, counting the specimens which 

 exhibit a given property and applying the method of calculation 

 alluded to in the note on p. 34 and completely expounded in 

 §§ 104-106. 



Unfortunately the theory of hereditary factors is hitherto 

 only applicable in those cases in which hybridization and culti- 

 vation of the hybrids are possible. When we deal, for instance, 

 with mosses, ferns and many other living organisms with which 

 hybridization cannot be carried out with certainty, or with 

 fossil species, we shall need another method. 



Therefore, in order to answer the needs of descriptive science, 

 I leave the hereditary factors out of account in the present 

 work, limiting myself to the study of the primordia. I try 

 to discern and to express the latter by measurement and to 

 collect in this way exact notions, by means of which it may be 

 possible to bring the inventory of hving nature into a more 

 useful form, and to throw more light upon the problems of 

 heredity and the origin of species. I avail myself as often 

 as possible of the information collected by the MendeUan 

 School. 



^ In other words, the property a is produced by the coexistence of both 

 factors A and C, the property b by the coexistence of B and C 

 2 See BATESON, loc. cit.. p. 98. 



^ For instance, in all the species of a genus, a family, etc. 

 * This subject is expounded in BATESON, loc. cit., passim. 



