EFFECTS OF IN-BKEEDIN-G Als^D CROSSBREEDII^G. 3 



) reconcile with the results in the only other recent extensive exper- 

 aent on inbreeding of mammals, namely, those which Miss King 

 3tained with rats. It will be shown, however, that the two exper- 

 aents are complementary rather than contradictory. It may 

 3 well to caU attention to the excellent summaries of the present 

 late of knowledge on the subject to be found in Miss King's series 

 ' papers and in "Inbreeding and Outbreeding" by East and Jones. 



PLAN OF THE EXPERIMENTS. 



An extensive investigation of the effects of inbreeding was planned 

 1906 by George M. Rommel, Chief of the Animal Husbandry 

 ivision of the Bureau of Animal Industry. The work was com- 

 enced in that year at the Experiment Station of the bureau at Be- 

 esda, Md., with guinea pigs as material. Since 1911 the experiments 

 Ave been carried on at the Experiment Farm of the Bureau of 

 aimal Industry at Beltsville, Md. Over 30,000 guinea pigs have 

 en recorded. The work has been conducted successively by Ralph 

 (Carr, Dr. E. H. Riley, F. R. Marshall, and the writer. Essentially 

 e same system of records has been kept throughout. On taking 

 large in September, 1915, the writer found the previous records 

 I excellent condition. In analyzing these and later data a great 

 •loimt of tabulation and calculation has been necessary. The 

 iter has been assisted successively by Walter J. Hall ahd Orson 



Eaton, to whose painstaking care in this laborious work the carry- 

 ; through of the project is in a large measure due. AU tabulations 

 Id calculations have been carefully checked. 



mSTORY OF THE GUINEA-PIG STOCK. 



Dr. E. C. Schroeder, superintendent of the experiment station at 

 tthesda, Md., has kindly furnished the following account of the 



J 'ly history of the stock : 



he history of the station's stock of guinea pigs is as follows: When I took charge 

 ) he experiment station of the bureau (at that time located at Benning Road and 

 ihteenth Street NE., Washington, D. C), during the summer of 1894, I found on 



I d about 250 to 300 guinea pigs, of all sizes and ages, about the history of which no 

 ■( )rds were available. The general character of the animals indicated that some 

 i- mpts had been made to breed special varieties, such as curly haired guinea pigs, 

 V te guinea pigs with black-smudged muzzles, long-haired guinea pigs, etc. 



s there was a superabundance of other work which lu-gently required attention 



II he station, I at once abandoned all attempts to breed guinea pigs of special types 

 .1 kinds, and made of the breeding pens a strict business project, with no other 

 )■ pose in mind than the production of a sufficient niunber of satisfactory animals for 

 H technical work of the bureau. I used the stock on hand, eliminating the fancy 



3s as much as possible, because they are less satisfactory than the plain, vari- 

 red, smooth-haired type for laboratory use. 



1 the year 1895, as nearly as I can remember, I purchased a nimiber of plain, 

 nary male guinea pigs, which, after a lengthy period of quarantine, were intro- 

 3d into the breeding pens. 



