116 THE BREEDING OF ANIMALS 



and spinal cord, particularly those which control the 

 act of coition, 1 diabetes and albuminuria are tojbe regarded 

 as causes of sterility. 



The potency of the semen of the male may be so weak- 

 ened by too frequent services by the stallion as to result 

 in sterility. The number and frequency of services 

 which can be required of a stallion and still retain the 

 full vitality of the sperm-cells varies greatly with different 

 individuals. An interesting contribution to this subject 

 is reported by Lewis : 2 A draft stallion was permitted 

 one cover daily for nine consecutive days. Samples 

 of the semen were taken to the laboratory in a warm steri- 

 lized receptacle. The number of sperm-cells to the cubic 

 millimeter in the semen from the first service was 131,750. 

 The number of sperm-cells decreased daily with consider- 

 able uniformity until the ninth service, when the number 

 suddenly diminished from 51,480 to 5840. The vitality 

 of the spermatozoa was determined by maintaining the 

 fluid at a uniform temperature and determining the num- 

 ber of viable sperm-cells at the end of a given period. 

 Thus when the semen was kept at a temperature of 31 

 to 35 C. it was found that five per cent of the 

 cells from the first service were aliVe after nine and five- 

 tenths hours. From the third service no cells were alive 

 after six hours. From the sixth service no cells were 

 alive after four hours, and from the eighth service no cells 

 were alive after three hours. In a second test a grade 

 stallion was bred eleven times on consecutive days. 

 The author summarizing this test concludes that : 3 

 " Approximately the vitality of the cells decreased one- 



1 Comer, "Diseases of the Male Generative Organs, " 1907. 



2 Lewis, Oklahoma Experiment Station, Bui. 96, 1911. 



3 See Marshall, "The Physiology of Reproduction." 



