2 HELEN DEAN KING 



of various stockbreeders on horses and cattle (Chapeaurouge, 

 '09; Anderson, '11) have shown conclusively that there is no 

 general physiological law forbidding inbreeding and that the re- 

 sults obtained depend very largely on the character of the stock 

 that is inbred. As Chapeaurouge has stated: 



Die Erfolge und Miserfolge nachster Inzucht hangen klar und 

 sicher nicht nur von der Gesundheit und Konstitution der Stammel- 

 tern und den ausseren Verhaltnissen ab, in welchem die Tiere gehalten 

 werden; sondern auch vor alien Dingen von der richtigen Auswahl der 

 Tiere zur Weiterzucht, welche nie die allgemeinen Bedingungen des 

 ziichterischen Zweckes gegeniiber den speziellen aus dem Auge lassen 

 darf. Je mehr die Haltung den nattirlichen Verhaltnissen oder den 

 Bedtirfnissen der Zuchttiere entspricht um so weniger sind iible Folgen 

 zu befiirchten. 



There are a number of questions of economic as well as of 

 scientific import which recent work on inbreeding does not 

 answer: Does close inbreeding, if carried on for a long period 

 of time, ever lead to degeneration if only the best animals, from 

 sound stock, are used for breeding? If degeneration does fol- 

 low from this kind of mating, does it affect merely the body size, 

 vigor, and fertility, or does it also influence body form and modify 

 the structure and action of the central nervous system? If no 

 evil results appear, can inbreeding be used to improve a race by 

 combining the best of the dominant characters with any de- 

 sirable recessive ones that may appear? Finally, does inbreeding 

 change the normal sex ratio, as Diising ('84) and others have 

 maintained? Taking advantage of the opportunity which the 

 animal colony of The Wistar Institute of Anatomy and Biology 

 afforded for carrying on an investigation that might answer 

 some of the above questions, a series of inbreeding experi- 

 ments on the albino" rat was started in the spring of 1909. 

 As the work, although still in progress, has already extended 

 over a period of eight years, it seems advisable that some of the 

 results obtained should be published, since they lead to rather 

 definite conclusions. The present paper, the first of a series, 

 gives a detailed account of the investigation, with an analysis 

 of the effects of close inbreeding on the growth and variability 



