138 
GENETICS: W. H. TALIAFERRO 
Proc. N. A. S. 
u King, H. D. 1916. The relation of age to fertility in rat. Anat. Rec, 11. 
12 Machens, A. 1915. Fruchtbarkeit und Geschlechtsverbaltnisse beim vered- 
delten L/andschwein. Berliner Tierartzliche Wochenschrift, 31. 
13 Miner, J. R. 1915. Fitting logarithmic curves by the method of moments. J. 
Agric. Res., 3. 
14 Minot, C. S. 1891. Senescence and rejuvenescence. First paper: On the weight 
of guinea pigs. J. Physiol., 12. 
15 Mumford, F. B. 1917. The Breeding of Animals. 
l6 Pearl, R. 1913. Note regarding the relation of age to fecundity. Science, N. S., 37. 
17 Pearl, R. 1914. On the law relating milk flow to age in dairy cattle. Proc. Soc. 
Exp. Biol. Med., 12. 
18 Rommel, G. M. 1907. Inheritance of litter size in Poland China sows. American 
Breeders Report 3. 
VARIATION AND INHERITANCE IN SIZE IN TRYPANOSOMA 
LEWI SI 1 
1. Life-cycle in the Rat and a Study of Size and Variation in 
"Pure Line" Infections 2 
By W. H. Taliaferro 
Department of Medical Zoology of the School of Hygiene and Public 
Health, Johns Hopkins University 
Communicated by R. Pearl, May 2, 1921 
The flagellate, Trypanosoma lewisi, is a non-pathogenic blood parasite 
occurring in various species of rats all over the world. It is known to be 
transmitted from rat to rat by the rat flea. This trypanosome was se- 
lected for the present work because it occurs in the latitude of Baltimore 
and the vertebrate and invertebrate hosts can easily be reared in the labor- 
atory. 
The general plan of the present work on size in T. lewisi is to make a 
careful study of size and variability in a pure line and then with this back- 
ground to attempt to explain the facts observed in infections occurring 
in nature. After a pure line infection was obtained the following ques- 
tions were attacked: (1) What are the mean and the coefficient of vari- 
ation? (2) Does growing the same "pure line" in different vertebrate 
hosts cause significant differences in the mean size or in the coefficient 
of variation? (3) Does passage of the "pure line" through the inverte- 
brate host cause significant differences in the mean or coefficient of vari- 
ation ? This question gives us a chance to test the possibility that passage 
of the "pure line" through the invertebrate host may cause a splitting 
up of the "pure line" into heritably diverse lines. After a study is made 
of these questions we can attack the final one: (4) Does an infection 
occurring in nature consist of a large number of "pure lines" such as has 
