The Bacterial Flora of Milk Held at Low Temperatures

Abstract

The value of milk and cream for human food, either alone or as constituents of more elaborate dishes, has led to efforts for their preservation for considerable periods of time. Such preservation is necessary in order to furnish a supply for places where the fresh product cannot be obtained, as on ocean steamships, or for a time of abnormal demand, such as that occasioned by the Fourth of July. The bacterial changes undergone by milk during its preservation at low temperatures have been made the subject of considerable study by Conn and Esten,1 and by Pennington,2 these investigators being preceded by Havemann,3 Schmidt-Nielson,4 Schmelk,5 Conradi and Vogt,6 Fischer,7 and Muller,8 who showed that certain bacteria can grow at a temperature as low as 00 C. The investigations of these earlier scientists consisted mainly in keeping various inoculated menstra at about 00 C. and making quantitative bacterial determinations at stated times. Their conclusions were that, altho growth does take place, it is comparatively slow. Conn and Esten showed that at 10 C. there is a period of from six to eight days during which there is no increase in the total number of bacteria in milk, and that when growth does start at this temperature the lactic bacteria fail to predominate over the other species, so that all types develop. They concluded that milk is not necessarily wholesome because it is sweet and that the species developing at this low temperature are more apt to be injurious than species developing at 200 C. Pennington concluded that at the low temperature (29-320 F.) employed in her experiments there were constantly present bacteria which formed acid and bacteria which acted on protein, the former