• The composition comprises preferably a calcium salt such as calcium chloride or calcium gluconate preferably in an amount of more than 0.5 mM and an amino acid such as L-histidine in an amount of more than 1 mM The amount could e.g. be chosen between 0.05 and 500 mM. Mono-or disaccarides such as sucrose or sugar alcohols could be added e.g. in an amount of 1 to 300 mg/ml.