34 



Scientific Proceedings (55). 



human heart, pointing out several interesting features in the 

 polygraphic records of the case. These records were of such a 

 nature that interpretation of them was very difficult and led to 

 doubtful conclusions. Since that meeting we have been fortunate 

 in securing excellent electrocardiograms of this heart through the 

 kindness of Dr. H. B. Williams. These records show that the 

 interpolated beats arise constantly in the right ventricle, and 

 probably in the right branch of the A-V bundle; the curves 

 indicate that the abnormal impulse travels to the basal part of 

 the left ventricle and thence to the apex, and that this path is 

 always the same; there is no evidence of retrogression to the 

 auricle, as was suspected from the mechanical tracings, but there 

 is evidence of depression of the conduction system, for the P-R 

 intervals of normal beats following the extrasystoles are often 

 considerably lengthened (we could not be certain of lengthened 

 As-Vs intervals in the polygrams). Phonocardiograms show 

 divided second sounds produced by the abnormal beats and 

 lengthened first sounds. A few compensating pauses have been 

 seen in the electrocardiograms. 



Aside from these new facts about the case, our previous report 

 needs no alteration. 



21 (838) 



The incidence of cancer in various strains of mice. 1 



By A. E. C. Lathrop and Leo Loeb. 



[From the Department of Pathology, Barnard Free Skin and Cancer 

 Hospital, St. Louis.] 



A number of investigators noticed the repeated occurrence of a 

 particular kind of cancer in animals living either in the same cages or 



1 These investigations are the outcome of plans for research which one of us 

 suggested about seven years ago; on that occasion we pointed out the necessity for 

 the study of possible hereditary and infectious factors in cane r directly in breeding 

 establishments. In accordance with these suggestions our investigations were 

 carried out in conjunction with Miss Lathrop in Granby, Mass., one of the most 

 extensive breeders of mice, who supplied at various times different laboratories in 

 this country with ordinary as well as with tumor mice, and from whom we obtained 

 about seven or eight years ago a mouse with a spontaneous tumor which we have 

 since propagated through many generations of mice and which was used in the 

 majority of our experiments. 



