138 MILK BACTERIA AND HEALTH. 



fermentative organisms cannot be doubted, inasmuch as no 

 other source of such toxic products is known. Moreover, in 

 a few cases there have been isolated from the poisonous 

 material certain bacteria capable of developing toxic products 

 similar to, if not identical with, those in the original sample 

 of ice cream (166). In one case of milk poisoning, also, 

 there has been isolated a bacterium producing, when used 

 in laboratory experiments, products which give rise to 

 symptoms similar to those of the original milk poisoning 

 (168). Such instances, however, are few at present because 

 of the rarity of the examples and the difficulty of obtaining 

 decisive results; but the fact that, in one or two cases, the 

 phenomenon has been positively traced to the development 

 of bacteria makes it almost certain that the whole series of 

 cases of poisoning from milk products must be attributed to 

 the development, in the milk, of certain unusual species of 

 bacteria which produce violent toxic poisons, and thus render 

 the milk unwholesome. 



Up to the present time no means have been suggested of 

 avoiding such occasional dangers. We do not know the 

 conditions under which they develop. Why one sample of 

 cheese will develop such poisons under conditions appar- 

 ently similar to those under which other wholesome cheeses 

 are kept; why some samples of ice cream are poison- 

 ous, and why some cans of milk develop unwholesome 

 qualities, we cannot say. In a few instances the trouble has 

 been attributed to the fact that the milk has been kept for a 

 considerable time in a damp, somewhat unwholesome room, 

 where there has been opportunity for contamination with 

 unusual bacteria and for a long period of growth. As has 

 been shown elsewhere, when milk products are kept at a low 

 temperature the lactic bacteria do not develop readily, while 

 other forms are more capable of growth. The cream which 

 is used for ice cream is occasionally kept for a considerable 

 time at a low temperature, and thus there is an opportunity 



