276 



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DISCUSSION 



Folley: I should like to make observations on two points arising out 

 of Dr. Popjak's paper. 



The first is that since the in vivo experiment on the lactating goat 

 which he described was done, our two laboratories have collaborated 

 with Professors Peeters and Massart of the University of Gent in an 

 experiment on the perfused isolated bovine udder. By means of the 

 apparatus of Peeters and Massart, two separated halves of a bovine 

 udder can be perfused simultaneously, with no mixing of the two circula- 

 tions. We have perfused one half of a lactating bovine udder with 

 1 mc. of [carfeoa^i/- ^*C]acetate and the other half simultaneously with 

 1 mc. of i*C-labelled bicarbonate. The specific activities of the milk 

 and udder fatty acids after two hours' perfusion are shown in Table I, 

 which is taken from Cowie et at. (1951). 



Table I 



Specific Activities of Glyceride Fatty Acids and Cholesterol from 



Milk and Udder Tissue after Perfusion with CHg^COONa (1 mc.) and 



NaHi^COg (1 MC.) (from Cowie et ah, 1951) 



(Specific activities expressed as 1 x 10"^ /iC. mg. C) 



These results confirm in general the conclusion drawn from the original 

 work on the live goat, that acetate is an important substrate from which 

 the mammary gland builds up fatty acid chains. It will be seen that 

 under the conditions of this perfusion experiment the mean specific 



