MASS. EXPERIMENT STATION BULLETIN 420 



CHART 1. 

 MORTALITY RATES 



FIRST 8 WEEKS 



2 5 



20 



°^ I 5 

 o ' ^ 



I 



UJ 



o 



ui 5 



0. 



1935 1936 1937 1938 1939 1940 1941 1942 

 YEAR HATCHED 



20 



I 5 



I 



CHART 2 



MORTALITY RATES 



8 WEEKS TO 6 MONTHS 



SEXES COMBINED 



1935 



1936 



1937 1938 1939 

 YEAR HATCHED 



942 



Two points are of vital interest in the consideration of the data: First, has 

 there been a progressive increase or decrease in mortality rate during the eight- 

 year period? Second, was there a significant difference in the mortality rates 

 in the four lines? 



The data (Table IB and Chart 2) show a consistently higher mortality rate 

 in males than in females during the period from 8 weeks to 6 months of age. 

 This is in agreement with the observ^ations of a number of workers. 



The mean mortality rates for all chicks in each of the four lines over the eight- 

 year period were fitted to a straight line by the method of least squares and the 



