cannot call a stored procedure from within another stored procedure

[Sherril Blackmon]

I have created a stored procedure to help debug stored procedures

CREATE PROCEDURE `WRITE_TO_LOG`(_STRING VARCHAR(5000))
BEGIN
START TRANSACTION;
INSERT INTO logging (LOG_STRING) VALUES (_STRING);
COMMIT;
END

but I am unable to use it:
CREATE DEFINER=`root`@`localhost` FUNCTION `Prepare_values_string`(valueString TEXT) RETURNS varchar(5000) CHARSET latin1
BEGIN
DECLARE _val TEXT;
DECLARE _pos INT;
DECLARE _TAB CHAR;
DECLARE _COMMA CHAR;
DECLARE _len INT;
DECLARE _return_ TEXT;

SET _TAB = x'0009';
SET _COMMA := x'0044';

IF ENDS_WITH(valueString) <> _TAB THEN
SET valueString := CONCAT(valueString, _TAB);
END IF;

SET _return_ := '';
SET _len = LENGTH(valueString);
aWhileLoop : WHILE _len <> 0 DO
SET _pos = locate(_TAB, valueString);
SET _val = substring(valueString, 1, _pos -1);
SET _val = quote(_val);
SET _return_ := concat(_return_, _COMMA, _val);
SET valueString := substring(valueString, _pos +1);
CALL WRITE_TO_LOG(valueString);
SET _len := LENGTH(valueString);
END WHILE aWhileLoop;

RETURN concat('(', _return_, ')');
END

I tried an example where a script created three stored procedures where the third called the first two and it worked like it should.
And, I was able to call the WRITE_TO_LOG proc from a sql script but not from another stored procedure.

Thank you for your help.