REPRODUCTION 45 



cells were alive at the temperature of 18 C., and 45 per cent 

 of the cells kept at a constant temperature of 26 were 

 still active. The sperm-cells from boars of several breeds 

 showed similar behavior and in every case the higher 

 temperatures were unfavorable. Semen kept at a tem- 

 perature of 31 to 32 C. and exposed to the diffused light 

 of the laboratory resulted in the death of practically all 

 the sperm-cells at the end of seven hours. A portion of 

 the same semen protected from the light by wrapping 

 in black paper showed 40 per cent of the germ-cells alive 

 at the end of the same time. The spermatozoa exposed 

 to direct sunlight for ninety minutes were all killed, while 

 the portion protected from direct rays of the sun showed 

 80 to 90 per cent alive at the end of the same time. 



46. Effect of too frequent breeding on the sperm-cells. 

 Lewis 1 found that the number of sperm-cells in the 

 semen collected from the first service of a vigorous stal- 

 lion was 428,000 to a cubic millimeter. The stallion 

 was permitted one service daily for nine days. The 

 number of sperm-cells diminished rapidly until there 

 were only 74,300 sperm-cells to a cubic millimeter at 

 the ninth service. The continuous and frequent service 

 of the stallion also resulted in weakening the vitality of 

 the sperm-cells. The semen from the first service kept 

 at constant temperature of 13 to 21 C. showed twenty- 

 five per cent of the sperm-cells alive after six-and-one-half 

 hours. The sperm-cells in semen collected from the 

 ninth service showed only five per cent of the cells alive 

 after six hours. Simple exposure to the air seemed to 

 have no deleterious effect on the vitality of the sperma- 

 tozoa. 



The standard of judging of the vitality of the sperm- 



1 Loc. cit., p. 35. 



