86 THE GERM-PLASM 



of an id, and also the number of determinants in a given species. 

 Unfortunately, however, we are completely ignorant on these 

 points, nor do we even know how many molecules take part in 

 the construction of a biophor : even the computed size of the 

 molecule is somewhat uncertain. 



The diameter of a molecule has been estimated at between 

 the i.Do.'i.iA.j th and the ii),oili.mjii th of a millimetre by four different 

 lines of reasoning, ' founded respectively on the undulatory the- 

 ory of light, on the phenomena of contact electricity on capillary 

 attraction, and on the kinetic theory of gases.'* O. E. Meyer 

 has calculated the size of a molecule ' from the properties and 

 behaviour of vapours. From the constant of friction and the 

 comparison between the space occupied in the liquid and gas- 

 eous conditions, together with tlie deviations from Boyle and 

 Mariott's law, we can approximately calculate, firstly, the volume 

 of all the particles contained within a given space ; secondly, 

 that of a single particle ; thirdly, the number of particles ; and 

 finally, the weight of a single particle.' The result of such a 

 calculation agrees with that given above. 



If we take the average diameter of a molecule to be o^KiiVmith 

 mm., and reckon that each biophor, which we will suppose to be 

 a cubical structure, is composed of i.ooo molecules, the biophor 

 would measure lo molecules in length. A row of 200 biophors 

 would therefore measure i /x, and 8,000,000 biophors would oc- 

 cupy the space of i cubic /x. A human blood-corpuscle measures 

 1 -I M- in diameter ; if we imagine it to be enlarged so as to form 

 a cube of 7.7 m- in diagonal length, this space would contain 

 703,000,000 biophors. Let us further assume that those por- 

 tions of the cell which, according to the facts at our disposal, 

 must contain the idioplasm, viz., the chromosomes, are mostly 

 a great deal smaller than the nucleus in which they are situ- 

 ated, and that the germ-plasm is composed not of o)ie but of 

 several ids, each of which contains all the biophors required 

 for the construction of the entire body, it will then be evident 

 that only a limited number of biophors can be contained in 

 one id. 



The chromosomes in the germ-plasm of Ascaris megaloce- 

 phala are the largest which are at present known to us. Each 



* Sir William Thomson, 'Popular Lectures and Addresses,' Vol. L, 



1889, p. 148. 



