STRUCTURE OF THE UDDER. 17 



milk prevented from running out, except under strong pres- 

 sure, by a contraction at its extremity. Following the tube 

 upward to the top of the teat, where all the branches centre 

 into one common channel, there is another contraction sup- 

 plied with a band of muscles, which is under the control of the 

 cow's will. Further up the tubes, where the branches have 

 connections, there are contractions of a similar kind, that 

 appear to be, at least partially, under the control of the will. 

 These contractions are kept closed all the time, except when 

 the cow makes a special effort to relax them, as when the 

 milk is being drawn. Upon handling the teats, the first effort 

 of the cow is to increase the stringency of these contractions, 

 drawing them so tight as to shut off the flow entirely ; but 

 after a minute or so, if all is quiet, she will slacken the con- 

 tractions, and let the milk flow down so it will press heavily 

 upon the teat. An expert milker can thus draw the milk in 

 a short time ; or, if a tube is inserted, it will flow out quickly 

 of its own accord. But this state of relaxation will not re- 

 main long. The cow will soon begin to draw up the slack 

 gradually, if all is quiet, and, tightening more and more, will, 

 after a little, cut off the flow entirely. She will do this the 

 more easily and effectually as the quantity in her bag dimin- 

 ishes ; and when the flow toward the last of the milking is 

 completely cut off, the milker may as well bid good-by to 

 what is left ; he cannot get it till the bag has been again filled, 

 and another relaxation induced. When such a case of cuttino; 

 off the last part of the milk occurs, the milk of the next 

 milking, if the cream rises in the bag, ought to be the richer for 

 it ; but I have not found it so. It is a curious circumstance, 

 that while one kind of fatty matter is being absorbed and 

 carried away into the general circulation, auother variety of 

 fatty matter is as constantly being formed to fill its place. 

 The new kind of fatty matter which is formed is not equal in 

 bulk to that which has been absorbed, but in some other 

 respects it is equal, and more than equal. 



In the curing of cheese, the changes which occur are now 

 known to be the effect of the action of the rennet which was 

 used to coagulate the milk. In the changes which occur in 

 the latter part of the curing process, it is known that a part 

 of the albuminous matter in the cheese is changed into fatty 

 3 



