536 



SCIENCE 



[N. S. Vol. XLIV. No. 1137 



employ a large proportion of scientific experts 

 are all on a gigantic scale is quite mistaken. 

 Even those which are on a gigantic scale were 

 small once; they have become large through 

 applying science. Some small works in this 

 country are highly scientific; some very large 

 ones are exactly the opposite. The chief cause 

 of manufacturing inertia is the mentality of 

 British business men, which is essentially prac- 

 tical and distrustful of ideas. But the shock 

 of war has undoubtedly disturbed them, and 

 there is some prospect of a change. It is 

 essential to success, as the committee admit. 

 " We recognize that unless the generality of 

 British firms can be induced to alter their 

 present attitude we shall have failed pro- 

 foundly in one of our appointed tasks." Re- 

 search has hitherto offered no career for able 

 and enterprising young men in this country. 

 So they have not gone in for it, and when a 

 manufacturer did want a man he had to go 

 abroad for him. It was a vicious circle. 

 But we believe that in the new prospect now 

 opening up the committee are right in advo- 

 cating the policy of increasing the supply 

 of men. The demand will follow. — London 

 Times. 



SCIENTIFIC BOOKS 



The Mechanism of Mendelian Heredity. By 

 T. H. Morgan, A. H. Sturtevant, H. J. 

 Muller and C. B. Bridges. Henry Holt 

 and Company, New York. 1915. 

 Students of genetics some six years ago 

 learned with lively interest that Professor Mor- 

 gan had discovered in the fly Drosophila am- 

 pelophila an example of inheritance parallel 

 to that seen in the well-known descent of color- 

 blindness in man. Substituting red eye and 

 white eye in the fly for normal color vision 

 and color-blindness respectively in man the 

 phenomena were exactly similar. Hitherto no 

 such case in an animal available for experi- 

 ment had been known. We were aware of 

 several instances, notably that of the moth, 

 Abraxas grossulariata, the pigmentation of the 

 silky fowl, and certain others in poultry, ca- 

 naries and pigeons, in which analogous de- 

 scents had been traced; but in all these the 



parts played by the sexes were reversed. From 

 this evidence indeed it had been proved that 

 in the moth and the birds the unfertilized eggs 

 are differentiated into two classes, those des- 

 tined to become females and those destined 

 to become males. Obviously enough it would 

 be inferred from the descent of color-blind- 

 ness that in man the sperm was similarly thus 

 differentiated into two such classes, destined 

 to form females and males respectively, a phe- 

 nomenon which Wilson and others had cyto- 

 logically demonstrated in various insects. At 

 this point the matter rested. 



With the discovery of the peculiarities of 

 Drosophila genetic research has passed into a 

 new phase. The animal breeds rapidly, going 

 through many generations in a year. It is in- 

 expensive to breed, and the families consist 

 of numbers which, relatively to those attain- 

 able in most subjects, are enormous. Since it 

 first attracted Professor Morgan's attention it 

 has been found to produce a long and intricate 

 series of factorial varieties, or " mutations " 

 as the authors prefer to call them, differing 

 in the color of eyes and body, the sizes and 

 shapes of the wings, and other respects, the 

 number of these differences being now com- 

 puted at more than a hundred. Professor 

 Morgan and a band of enthusiastic colleagues 

 set themselves with the utmost zeal to analyze 

 the inter-relations of this mass of factors. 

 Half a million flies have been bred, with the 

 result that the data respecting the genetics 

 of Drosophila in quantity now surpass those 

 obtained from any other animal or plant. The 

 advances made are on any estimate many and 

 of quite exceptional significance. That much 

 is certain. If we go further, and accept the 

 whole scheme of interpretation without re- 

 serve we are provided with a complete theory 

 of heredity, so far as proximate phenomena 

 are concerned. 



We may perhaps best approach the sub- 

 ject by reference to a class of facts with which 

 all investigators are now familiar. Of the 

 factorial differences detected in Drosophila, 

 many of the more important were soon shown 

 to be sex-limited, as we used to call it, the 

 " limitation " being to males, just as in color- 



