Vol.. 7, 1921 
GENETICS: W. H. TALIAFERRO 
163 
VARIATION AND INHERITANCE IN SIZE IN TRYPANO- 
SOMA LEWISI 
II. The Effects of Growing "Pure Lines" 1 in Different Verte- 
brate and Invertebrate Hosts and a Study of Size and 
Variation in Infections Occurring in Nature 
By W. H. Taliaferro 
Department op Medical Zoology op the School of Hygiene and 
Public Health, Johns Hopkins University 
Communicated by R. Pearl, May 2, 1921 
In our first report 2 we demonstrated that Trypanosoma lewisi reaches 
an adult stage in the course of the infection in the rat in about 25 days, 
and once this stage is reached there is practically no division or growth. 
In consequence of the elimination of growth factors from the compu- 
tations it was found that the coefficient of variation in the "pure line" 
was very low if it was computed during this adult period. The questions 
which now arise are: (1) Does growing the same "pure line" in different 
vertebrate hosts cause significant differences in the mean or the co- 
efficient of variation? (2) Does passage of the "pure line" through the 
invertebrate host cause any significant differences in these constants? 
Our attention will be directed especially toward the coefficient of vari- 
ation as this will give us an opportunity to ascertain whether or not there 
is a splitting up of the "pure line" into heritably diverse lines following 
such passage through the invertebrate host. With this background our 
final question is: (3) Does an infection occurring in nature consist of a 
large number of "pure lines" such as have been described in free-living 
protozoa, which differ among themselves but are per se constant in size? 
It is to be emphasized at this point that in all of the following work 
the measurements and computations were made on or after the 30th day 
of the blood infection. As the adult stage is always reached by the 25th 
day this is well into the adult period and effectually eliminates growth 
factors. The six measurements of size used in this work have already 
been given in our first report (see figure 1). They consist of the following 
distances: (1) Posterior end to parabasal body, (2) parabasal body to 
nucleus, (3) nucleus to anterior end, (4) anterior end to end of flagellum, 
(5) total length which includes measurements 1-4, and (6) width. 
Effect of Growing the Same "pure line" in Different Vertebrate Hosts. — 
The twoconstants in which we are interested in this connection are the size 
as indicated by the mean and the variability as indicated by the coefficient 
of variation. In all of the experiments the constants were worked out 
for all six measurements but in this brief report we will only deal with 
those for total length. Let us first consider the mean. The questions 
are: Does growing the same pure line in different individuals of the same 
