F. S. Hammett 385 
SUMMARY. 
1. In the determination of ammonia or urea in placenta tissue 
the use of solid potassium carbonate offers opportunity to main- 
tain a minimum volume of the aerated mixture. 
2. 5 gm. of the solid potassium carbonate are sufficiently effec- 
tive in liberating the ammonia present in amounts of tissue rang- 
ing from 4 to 10 gm. and suspended in 10 to 15 ce. of water. 
3. 2 minutes of mild aeration followed by 28 of vigorous pas- 
sage of air completely drives over all the ammonia present in the 
amounts of tissue ordinarily used for analysis. 
4. The use of a mixture of equal parts of amyl alcohol, toluene, 
and ethyl alcohol prevents foaming in test-tube and flask. 
5. The ammonia content of tissue increases during standing for 
% hour. 
6. In the direct determination of urea in tissues by means of 
the urease method it is imperative that simultaneous analyses 
be made for the ammonia fraction. The tissue samples from 
which the ammonia values are to be obtained must be allowed to 
digest for the same length of time and under the same conditions © 
as do those specimens from which the urea is determined. 
Through the courtesy of Professor Otto Folin the work re- 
ported in this paper was carried on in the Biochemical Labora- 
tories of the Harvard Medical School. 
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QOonrwnrye 
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