July 6, 1917] 



SCIENCE 



19 



to designate the food requirement of a family 

 of five, containing three children whose ages 

 are between eight and sixteen. The diet pro- 

 vides 12,500 calories, contains 375 grams of 

 protein, and cost one dollar and six cents per 

 day in July, 1916. Of this, twenty-four per 

 cent, was spent for bread, thirteen per cent, for 

 milk, fifteen per cent, for meat, and the rest 

 for seventy other articles. The bread ration 

 contained 4500 calories or 35 per cent, of the 

 total energy value of the food. This kind of 

 information is of highest value to the house- 

 wife of limited means and can be successfully 

 applied by any intelligent person. 



" The Mothercraft Manual," by Miss Mary 

 L. Eead (Little, Brown and Company, 1916), 

 presents, in language which is a delight, mod- 

 ern as well as old world knowledge helpful in 

 the, creation of the best environment for the 

 family and describes the care, nutrition and 

 development of the child. 



Graham Lusk 



SPECIAL ARTICLES 



THE THEORY OF SEX AS STATED IN TERMS OF 

 RESULTS OF STUDIES ON PIGEONS^ 



At the 1911 meeting of this society, in 

 Princeton, I first made known the fact that the 

 sex of pigeons had been experimentally con- 

 trolled by Professor Whitman. The main fact 

 of method being briefly that from a family 

 cross practically only males, and from a generic 

 cross nearly all males, are produced ; but if, by 

 special means the birds of generic crosses are 

 forced to excessive reproductive overwork then 

 the earlier eggs of such a series produce mostly 

 or only males, while the later eggs — from the 

 end of the series— will produce mostly or only 

 females. At the same time and place I made 

 to this society a first report upon the nature of 

 the results of my own studies upon the ova of 

 some of these sex-controlled series. These re- 

 sults then indicated — to quote from the pub- 

 lished abstract of that paper- — 



1 Paper read December 28, 1916, before the 

 American Society of Zoologists (New York Meet- 

 ing)- 



2 Science, N. S., Vol. XXV., No. 899, pp. 462- 

 463; March 22, 1912. 



that eggs (yolks) of smaller size, higher water-eon- 

 tent and smaller energy-content (i. e., fewer \mits 

 of physiologically available energy) can be corre- 

 lated with maleness in the offspring. That eggs 

 (yolks) of larger size, lower water-content and 

 greater energy-content can be correlated with fe- 

 maleness in the offspring. 



The later results, which I have from time to 

 time presented before this society and else- 

 where, have fully confirmed and much ex- 

 tended the evidence for that early announce- 

 ment of the nature of the germinal differences 

 which characterize the two sexes. 



Though all of the several lines of study that 

 I have carried out on the doves and pigeons 

 have thrown light on the nature of germinal 

 and adult sexual difference most of these lines 

 of study were primarily designed to test the 

 possibilities of selective fertilization, differen- 

 tial maturation and elective elimination of ova 

 in the ovary as alternatives of a true sex-re- 

 versal or control. In view of the well-estab- 

 lished fact that the hetero-gametio sex produces 

 germs of two kinds — a sex-chromosome being a 

 differential already recognized — it has seemed 

 obligatory to supply decisive tests for the possi- 

 bilities just named. This has all been thor- 

 oughly done in the pigeons ; the result has been 

 made possible because the female here is the 

 hetero-gametic sex, producing male and fe- 

 male ova, and we have here learned to identify 

 each of the two kinds. In these forms Whit- 

 man controlled sex and clearly demonstrated 

 the methods of control. In these same forms I 

 have for six years repeated the control and 

 fully confirmed the method. In addition I 

 have obtained adequate proof of the reality of 

 the sex-control as against the above-mentioned 

 alternatives and have further shown that in 

 this material sex is a matter of essentially all 

 gradations. And, of signal and unique im- 

 portance is the fact that all, or at least many, 

 gradations of sex are obtained from the same 

 pairs of parents. The outlines of these find- 

 ings have been published in several short papers 

 beginning in 1911 f the entire body of evidence 



3 See under note 2 ; and, Carnegie Year Book, 

 1913; Science, Vol. 39, 1914; Bull. Amer. Acad, 

 of Med., A''ol. XV., 1914; Amer. Nat., Vol. L., 

 July, 1916. 



