52 EMBRYOLOGY 



centrated in a thick suspension in order to survive for an appreciable length 

 of time. If diluted with fluids they lose their fertilizing power very rapidly. 

 Another important factor is the hydrogen-ion concentration of the medium. 

 If the sperm are made more alkaline than their normal environment, they 

 become very active, but on the other hand, they do not live as long. This is 

 a repetition of the fact that if the sperm are very active they use up their 

 reserve supplies of energy and die early. Recall that the sperm contain a 

 substance which paralyzes their own activity. 



Animal breeders have made a study of fertilization, and artificial insemina- 

 tion in domestic animals is quite common. If sperm are concentrated in their 

 own fluids they will remain active for many hours, and various artificial 

 fluids have been devised to prolong activity. Sperm can be sent airmail across 

 country quite easily. They can then be injected into the female and fertiliza- 

 tion will occur. A number of variables have been worked out by the breeders. 

 The condition of the female and the time of ovulation have to be known, of 

 course. The age of the sperm is a factor which determines whether or not 

 fertilization will be normal. The concentration of sperm is extremely im- 

 portant. If it drops below a critical point no fertilization will occur although 

 millions of sperm may be present. Some observations indicate that the same 

 thing is true for human sperm. When the concentration of the sperm drops 

 below sixty million per milliliter a man is often sterile. It seems that 

 although there are plenty of sperm and they are active there are not enough 

 to create the situation necessary for fertilization. 



Another factor in artificial fertilization is the temperature at which the 

 sperm are kept. The sperm of even a warm-blooded animal will survive 

 longer if the temperature is lowered. Also, as in the sea urchin, the hydrogen- 

 ion concentration is important, and various fluids have been developed for 

 addition to the sperm before their injection into the female. The concentra- 

 tion of carbon dioxide is important. Sperm, by producing carbon dioxide, 

 anesthetize themselves and reduce their own activity, and this condition pro- 

 longs their life. 



In the actual practice of artificial insemination bull sperm are collected 

 in an artificial vagina warmed to a little above body temperature. The 

 artificial vagina is a water-jacketed rubber tube with a collecting bottle at 

 one end. The volume of semen in a single ejaculate is about 4.5 milliliters, 

 and the concentration of the sperm about 800 million per milliliter. Such a 

 sample of semen may then be used to inseminate about 45 cows. This single 



