IIO PRACTICAL DAIRY BACTERIOLOGY 



and these bacteria that love the cool temperatures are growing 

 all the time, so that in the end they will be present in large 

 numbers and will produce a quantity of toxic products. Now, 

 if the cream is made into ice cream when the next hot days 

 appear, the toxins which have been developing may cause among 

 those eating the cream a violent intestinal disturbance. Little 

 more is known concerning this trouble than the facts here 

 stated. The cause is probably the development of toxic germs 

 in cream kept at fairly low temperatures unchecked by the 

 growth of lactic germs, which would at a higher temperature 

 have prevented their development. 



It must be emphasized, however, that if these troubles do 

 come from such a source, it is not the mere presence of numbers 

 that produces trouble. As already mentioned, sour rnilk and 

 buttermilk are wholesome products and have never been sus- 

 pected of causing diarrheal troubles; yet they contain bacteria 

 in prodigious quantities. From this it will follow, of course, 

 that there are some kinds of bacteria whose presence in milk 

 is deleterious and others whose presence is harmless. What 

 types of bacteria are concerned in producing these toxins, we 

 do not know at present. It is a growing belief that the bacteria 

 concerned belong to the putrefying class. Putrefying bodies 

 certainly do frequently show the presence of toxins, and it 

 would be natural to assume that milk in which such germs are 

 growing would contain enough of the poisonous bodies to pro- 

 duce a toxic poisoning in children. We have already learned 

 that the putrefactive bacteria frequently liquefy gelatin and are 

 consequently easily detected on common gelatin plates. Hence, 

 we should be led to throw under suspicion any milk that shows 

 large numbers of liquefiers. On the other hand, it is quite cer- 

 tain that the lactic acid bacteria are not responsible for these 

 troubles. Indeed, the presence of lactic acid bacteria prevents 

 the growth of the putrefactive forms, and when the acid type 

 becomes very abundant, as high as hundreds of millions per c.c., 



