356 CHEMISTRY: W. A. NOYES 
Weighted mean reproductive indices for matings of individuals of the specified combined ages 
Combined ages of mated individuals 
when mated Cases Weighted mean RI 
2 years 796 13.083 
3 years 190 11.121 
4 years 113 11.119 
5 years 12 7.458 
The cases are too few to give reliable results after a combined age 
of four years. Up to that point, however, what occurs is this: There 
is a significant drop in reproductive ability as we pass from a combined 
age of two years for the mated birds to three years. In passing from 
three years to four there is no significant change in reproductive ability. 
In passing from a combined age of four years to that of five years there 
is a large drop in the net reproductive ability of the mating. 
All of these figures agree in indicating that in the strain of the domestic 
fowl with which this work was done there is nothing approaching that 
law of fertility which has been found to hold for mammals, as pointed 
out at the beginning. Instead we find a steady and progressive decline 
in fertility after the first breeding season. 
^ Marshall, F. N. A., The Physiology of Reproduction, London, 1910, xvii + 706 pp. 
2 Pearl, R., Science, New York, N. S., 37, 1913 (226-228). 
3 King, H. D., Anat.Rec, Philadelphia, 11, 1916 (269-289). 
^Pearl, R., /. Exp, ZooL, Philadelphia, 13, 1912 (155-268). 
complete and detailed report of this work will appear presently in Genetics. 
A KINETIC HYPOTHESIS TO EXPLAIN THE FUNCTION OF ELEC- 
TRONS IN THE CHEMICAL COMBINATION OF ATOMS 
By William A. Noyes 
DEPARTMENT OF CHEMISTRY. UNIVERSITY OF ILLINOIS 
Read before the Academy, April 16, 1917 
Beginning with Davy^ and BerzeKus, during the first part of the nine- 
teenth century chemists generally accepted the theory that chemical 
combination is due to electrical forces, but when Dumas discovered the 
chloroacetic acids in which chlorine atoms, supposedly negative, replace 
positive hydrogen atoms it was believed that the theory had been shown 
to be false and it was practically abandoned. Following this, for fifty 
years or more, a theory of valence which took no account of electrical 
forces was developed and while occasional reference was made to posi- 
tive and negative atoms and groups, no definite meaning in an electrical 
sense was attached to these expressions. Helmholtz in his Faraday 
lecture in 188P drew the attention of chemists once more to the very 
