Several synthetic mixtures of natural and racemic crystalline amino acids suitable for the daily nitrogen requirement are tested in dogs for their tolerance upon intravenous injection.

Certain mixtures of the ten essential amino acids plus non-essential amino acids exclusive of glutamic acid are accepted without any obvious sign of disturbance even at rates above 10 mg. nitrogen per kilo per minute for quantities greater than 300 mg. per kilo. One such mixture consists in parts per 100 of dl-threonine 7, dl-valine 15, l(-)-leucine 10.9, dl-isoleucine 9.9, l(+)-lysine· HCl·H2O 10.9, dl-tryptophane 3, dl-phenylalanine 9.9, dl-methionine 6, l(+)-histidine·HCl·H2O 5, l(+)-arginine-HCl 5, glycine 9.9, dl-α-alanine 4, dl-serine 2, l(-)-cystine 0.5, and l(-)-tyrosine 1. In addition other well tolerated mixtures included the prolines.

When glutamic acid, natural or racemic, is included in similar mixtures vomiting reactions frequently occur at nitrogen rates above 4 mg. per kilo per minute. Vomiting almost always occurs on the first daily injection containing glutamic acid and usually on any subsequent injection containing more than 100 mg. glutamic acid per kilo unless given very slowly.

Upon the addition of glycine certain mixtures of the ten essential amino acids show an improved tolerance.

Two casein digests tested usually produced vomiting at injection rates above 2 mg. nitrogen per kilo per minute, probably because of their glutamic acid content.

No serious reaction has ever occurrred to any mixture of amino acids or casein digest tested. Elimination of minor reactions such as vomiting appears possible and desirable for greater usefulness of these solutions in parenteral feeding.

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