A HORMONE FOR GESTATION 



covered another action of the corpus luteum. To make this 

 clear let us imagine an experiment such as is shown in Fig. 17. 

 A rabbit is killed, the uterus is removed, and a portion of one 

 horn is suspended in a cylinder of salt solution so that one 

 end is tied down and the other is fastened to a writing lever 

 that writes on a revolving drum. The salt solution is kept at 

 body temperature by standing in a bath of warm water. 

 Oxygen is bubbled through the salt solution, and a little sugar 

 is put into it as food, providing energy for the tissues. The 

 whole thickness of the uterus, except its inner lining, is com- 

 posed of involuntary muscle, as explained on page 48. Placed 

 in an apparatus of the sort just described, which imitates the 

 natural conditions within the body, any such piece of living 

 involuntary muscle, whether from the uterus, intestine, stom- 

 ach, bladder, blood vessels, or elsewhere, will undergo rhyth- 

 mic contractions every minute or two and will write them on 

 the revolving drum as shown in the illustration. The experi- 

 menter, if he likes, can induce larger, more sudden contrac- 

 tions by putting into the salt solution one or another of those 

 substances that are known to stimulate involuntary muscle. 

 A drop of adrenalin solution will make the uterine muscle pull 

 so strongly that it will almost yank the lever ofF the drum. So 

 will a drop of pituitrin solution (subject to a very important 

 reservation which is about to be mentioned) — indeed, pitu- 

 itrin is such a powerful stimulant of uterine muscle that it is 

 often used by obstetricians to make the human uterus contract 

 after childbirth. 



Knaus found that the uterus of a pregnant rabbit, set up 

 in salt solution as described, will not react to pituitrin. He 

 had just learned this when the first reports of the isolation of 

 progestin reached Austria ; he made up some crude progestin 

 (the first in Europe) and found that when he gave this by 

 injection to a castrated adult rabbit for 5 days, the uterus 

 became absolutely insensitive to pituitrin, exactly as if she 

 were pregnant. 



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