No. 633] SHORTER ARTICLES AND DISCUSSION 371 



Instituut and ourselves, that the Norway rat, which is the com- 

 mon rat in most parts of Holland, was practically, if not wholly, 

 absent from parts of Friesland. In these parts Mus rattus is 

 the common rat. Whereas Mus norvegicus succumbs readily to 

 an ingestion of the broth culture as prepared by the Institute, 

 we found the Mus rattus animals immune. Before we started for 

 Java, we tried the pathogenic influence of the culture as fur- 

 nished to farmers, on some of our cultivated rats of the Mus 

 rattus group, on request of our ministry of colonial affairs. The 

 rats were fed on a broth culture of a virulent strain of para- 

 typhoid and bread, at the Serum-institute, and they remained in 

 good health on this diet. The same culture killed practically all 

 Mus norvegicus rats in a few days. 



To our great regret we have never yet succeeded in obtaining 

 hybrids between the two groups of rats, norvegicus and rattus, 

 and for this reason the inheritance of this very marked immunity 

 of Mus rattus, or in other words predisposition of Mus norvegicus 

 can not be studied. We know of no case in the literature, of an 

 investigation of the inheritance of immunity to bacterial disease 

 in animals. 



As is well known, Biffen found a case of the inheritance of 

 resistance to rust in wheat, in which the difference between im- 

 mune and easily infected plants was proved to be due to pres- 

 ence or absence of one single gene. William Orton and Webber 

 have since found almost similar instances in cotton and water- 

 melons. 



So far as known to the authors, the following case of the in- 

 heritance of immunity, or predisposition for a microbial disease 

 in animals is the first one studied so far. 



From Nagasaki, Japan, and Hong Kong, China, we brought 

 along some stock of a very minute domestic mouse. These mice 

 evidently belong to the same group as the commonly imported 

 oriental Waltzing mice. As a matter of fact, our Japanese ani- 

 mals of the second importation produced some waltzing offspring. 

 We used this material for a few series of experiments on the in- 

 heritance of weight, one series starting from the only fertile 

 H'-iiLT Kong female, and the others from diverse combinations of 

 the Nagasaki strain with large white mice. These white mice are 

 of a pure-bred strain used by T. B. Robertson in his experiments 

 on growth. We produced numerous hybrids, great numbers of 

 F 2 animals, and further we are grading back the hybrids both 

 to the dwarf and to the heavy strain. For our work individual 



