164 
GENETICS: W. H. TALIAFERRO 
Proc. N. A. S. 
species of rat produce significant differences in size? Does growing the 
same "pure line" in different species of rats produce any greater differences 
in size than in the first case of individuals belonging to the same species? 
It would have been interesting to grow the "pure line" in other verte- 
brates as well as in rats but T. lewisi is not normally infective to any other 
vertebrate. To test the first of these questions we used individuals of 
the albino rat and for the second question we used individuals of the 
black and the Norway rat. At the outset it may be definitely said that 
the differences which were obtained on growing the "pure line" in differ- 
ent species of rats were in no way more significant than the differences 
obtained by growing the "pure line" in different individuals of the same 
species. The greatest difference in mean size 3 was obtained when the 
same "pure line" was grown in the albino rats 46 and 90. In the former 
the mean length was 32.080 ±.052 and in the latter 30.769 ±.057, which 
gives us a difference of 1.311 ±.077. The mean lengths obtained in 
twelve other experiments lie between these limits. While a difference of 
this character, which is 16.8 times its probable error, is undoubtedly 
significant the question immediately arises as to whether such a difference 
is due to differences in the blood of different rats or to a personal variation 
in making the measurements. A definite answer cannot be given to 
this question at the present time although experiments are being carried 
out to ascertain, if possible, which is the determining factor. As, however, 
this is the greatest difference obtained in twelve experiments, we may say 
that growing the same "pure line" in different rats probably causes sig- 
nificant differences in mean size, but in any case these differences are 
small. Even if these differences are significant there is no evidence, at 
present, that they are due to inherited diversities, but are simply due to 
differences in environment. 
In regard to variability, the chief thing of interest is the fact that passage 
of the "pure line" from rat to rat by blood inoculation has no effect on 
the coefficient of variation. Take, for example, the following experiment. 
The coefficient of variation for total length in the "pure line" as grown in 
rat 116 was 2.77 ±.13%. After four passages through white rats this 
line was grown in rat 204 where the coefficient of variation was found to 
be 2.60 ± .12%. The difference between these two coefficients is .17 ±.18% 
which certainly is not significant. Several other experiments gave simi- 
lar results and an experiment is being carried out now in which the "pure 
line" is undergoing numerous transfers from one rat to another. The 
fact that passage of the pure line through rats has no effect on the co- 
efficient of variation is in marked contrast to conditions found after pas- 
sage through the invertebrate host. 
Effect oj Passing the "pure line" through the Invertebrate Host. — While 
T. lewisi can be experimentally transmitted by several species of ecto- 
