Voiv. 6, 1920 
ZOOLOGY: CHEF LIN AND RETTGER 
423 
of rugose is recessive to the sterility of both glazed and wax. In the 
glazed-wax hybrid a similar relation holds for the somatic effect, glazed 
being dominant to wax. The high degree of sterility in both homozygous 
parent forms here, however, would naturally call for the observed sterility 
of the hybrid and eliminates the question of dominance with respect to 
this feature. 
From the above standpoint sterility in the rugose-glazed and rugose 
wax hybrids is accounted for by assuming the dominance of sterility in- 
stead of assuming an incompatibility as was done in the previous paper 
when only the rugose-glazed hybrids were known. The present explana- 
tion calls for the occasional occufrence of fertile hybrids between rugose 
and glazed to correspond to the occasional fertility in pure glazed females. 
No such fertile hybrids have been obtained thus far, but this may be due 
merely to chance, since only a very few of them would be expected in the 
number of females tested. This conclusion is made still more probable 
by the occurrence of the one fertile hybrid between rugose and wax. 
1 These Proceedings, 3, 1917 (673). 
2 These three characters are almost certainly allelomorphs, although the sterility of 
the hybrids and the dominance of the normal somatic constitution of rugose females 
makes it difficult to demonstrate the fact for the latter character. See Metz, C. W., 
Genetics, 3, 1918 (116). 
3 The females were tested both singly and in mass cultures. The use of some mass 
cultures prevents recording the exact number of flies actually tested, for in these a few 
females may have died before they had a chance to breed. 
* In each case these are such as to indicate fertihty, not contamination or non-dis- 
junction. In one case both parents were glazed, the offspring being 3 glazed females 
and 5 glazed males. 
It is difficult to obtain accurate determinations of the relative degrees of fertihty 
of the males in these cases, for even the wax males breed fairly well, but in general the 
relations seem to be as described. 
6 Since the characters are sex linked and apparently allelomorphic no truly "hybrid'* 
males can be obtained. 
^ In this and the preceding experiment offspring were obtained from two or three 
other bottles, but they were such as to indicate that they probably came from females 
heterozygous for one factor only, due to non-virginity or contamination. 
STUDIES ON THE TRANSFORMATION OF THE INTESTINAL 
FLORA, WITH SPECIAL REFERENCE TO THE IMPLANTA- 
TION OF BACILLUS ACIDOPHILUS. 1. FEEDING EX- 
PERIMENTS WITH ALBINO RATS 
By Harry A. Chepun and Leo F. Rettger 
BacterioivOgicaiv Laboratory, Yale University 
Communicated by L. B. Mendel, May 28, 1920 
The type of bacteria developing in the alimentary tract may be in- 
fluenced in a noteworthy manner, not only through special alterations 
