io6 Society for Experimental Biology and Medicine. 



recommend such a combination except for cases where the amount 

 of available urine is small. 



In order to obtain reliable results by this method it is neces- 

 sary to observe certain precautions. 



No time should be wasted after the alkali has been added to 

 the standardized iodine solution because the potassium hypoiodite 

 in the latter changes gradually to potassium iodate which is not 

 available for the formation of iodoform. The alkaline iodine solu- 

 tion must not touch rubber. The absorption tube must therefore 

 not consist of two tubes joined by a rubber stopper as I have here- 

 tofore used them in ammonia determinations but must be con- 

 nected by the glass blower. Eimer and Amend have made me 

 some excellent tubes suitable for this purpose. Finally no one 

 should attempt to use the method on unknown solutions or urines 

 until he has satisfied himself that he can get accurate figures with 

 known acetone solutions. Such solutions can be made and stand- 

 ardized in a few minutes by direct titration with the iodine and 

 thiosulphate solutions. Ten c.c. of pure acetone diluted up to 

 one-fourth of a liter and twenty c.c. of this solution diluted to 

 half a liter makes a suitable test solution of acetone. 



The addition of an excess of sodium chloride as described 

 above is important and should not be omitted. Acetone is insol- 

 uble or at least very little soluble in saturated sodium chloride 

 solutions. 



I am now investigating the acetone and diacetic acid contents 

 of diabetic urines by the help of this method. Most such urines 

 even when rich in diacetic acid contain surprisingly little acetone. 



73 (216) 



On magnesium and contractile tissues. 

 By Percy g Stiles. 



[From the Biological Department of the Massacliusetts Institute of 



Technology^ 



The experiments reported extend and confirm the findings of 

 Meltzer and Auer. Magnesium is found to have a direct inhibitory 

 effect on automatic tissue (plain and cardiac muscle) and a depress- 

 ing effect upon the irritability of the non-automatic striped muscle. 



