ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 453 



It seems to come to this, that divergent conchisions are in part dut- 

 to the data utilized. "A study of albinism alone would lead one to 

 believe in the fixity and constancy of Mendelian genes, and the im- 

 possibility of modifying them by selection. A study of white-spotting 

 leaves one with the unshakable conviction that this form of gene is 

 plastic and yields readily to selection. Where only genes of the former 

 sort are involved, the principle of the pure line is applicable ; where 

 genes of the latter sort are involved, it is not applicable." 



Castle inclines to the view that in the smaller mammals, which he has 

 particularly studied, very few characters can be safely referred to the 

 agency of perfectly stable genes. Very important is his conclusion that, 

 " aside from colour, there are very few valued economic characters in 

 our domestic animals which are not inherited after the manner of 

 blends." 



In conclusion. Castle points out that, " in the case of such characters 

 as white-spotting in mammals, it is evident that a change in the mean of 

 the character in a particular direction in consequence of selection actually 

 displaces in the direction of selection the centre of gravity of variation, 

 so that in a very true sense selection makes possible further variation 

 in that particular direction." The same is probably true as regards 

 protein-content and oil-content in the Illinois University Indian corn 

 experiment. 



At the same time, it will be recognized that selection, whether 

 natural or artificial, is, as the mutation theory rightly holds, primarily 

 an agency for the elimination of variations, not for their production. 

 It can only act on variations actually existing ; it cannot initiate new 

 lines of variation ; but it can continue and extend variation already 

 initiated by shifting in the direction of selection the centre of gravity 

 of variation. It is limited to effecting change in existing types of 

 organisms ; it helps them along lines in which they show a tendency 

 spontaneously to vary. 



Fundamental Biological Law.* — H. F. Osborn suggests the follow- 

 ing as " the most fundamental biologic law which can be expressed from 

 our existing knowledge " : — " In each organism the phenomena of life 

 represent the action, reaction, and interaction of four complexes of 

 physico-chemical energy, namely, those of (1) the inorganic environ- 

 ment, (2) the developing individual (cytoplasm and somatic chromatin), 

 (a) the germinal or hereditary chromatin, and (4) the organic environ- 

 ment. Upon the resultant actions, reactions, and interactions of each 

 organism selection is constantly operating whenever there is com- 

 petition with corresponding actions, reactions, and interactions in other 

 organisms." 



Toxicity of Serum of Mursena helena.t— W. Kopaczewski has made 

 experiments showing the extreme toxicity of the serum of this eel. The 

 results of sub-cutaneous and intra-peritoneal injections of guinea-pigs, 

 rabbits, and dogs showed very rapid action. A single dose was some- 



* Proc. Nat. Acad. Sci., U.S.A., iii. (1917) pp. 7 9. 

 t Comptes Rendus, clxi. (1917) pp. 963-4. 



