76 CONFERENCE ON MILK PROBLEMS 



sources. Can anything but pasteurization protect against 

 the infectious material that may be introduced into milk from 

 such individuals? 



We must bear in mind that the infection of milk is a very 

 different matter from the infection of other articles of food. 

 Milk is the only liquid article of human food that is at one 

 and the same time an ideal culture medium for micro-organisms 

 and that is very extensively used in a raw state. Other arti- 

 cles of food may also become infected, but if they are solid and 

 have firm, dry surfaces, like bread for example, as this is 

 an article that can in a measure compare with milk relative to 

 the extensive and practically indispensable need for it, the 

 disease germs remain on the exterior, where they are ex- 

 posed to the potent germicidal action of light and do not multi- 

 ply. Germs deposited on solid food that has a moist surface 

 may multiply, but the multiplication is slow compared to that 

 which occurs in milk, and, furthermore, most solid articles of 

 food that have moist surfaces are washed or exposed to the 

 sterilizing action of heat shortly before they are eaten. In 

 milk the germs not only find an excellent culture medium, but 

 they sink into it and are protected by its opaque character 

 from the action of light, and when they grow the rapidity of 

 multiplication is not limited as on a solid medium by the 

 formation of stationary colonies. 



As to the danger from those who are in the early stages of 

 infectious diseases, before a diagnosis has been made, or even 

 before the person is conscious that his health is declining, it 

 is well to remember that all our infectious diseases have a 

 period of incubation or a period of time that elapses between 

 the moment of infection and the visible development of symp- 

 toms. Just how soon during the period of incubation an in- 

 dividual becomes a source of danger to those who are exposed 

 to him is a subject about which we know very little. If we 

 take a disease like diphtheria, the germs of which multiply in 

 milk, we know that its diagnosis frequently depends on our 

 ability to obtain cultures of diphtheria bacilli from the pa- 

 tient's throat, a region from which germs are easily expelled 

 during coughing, sneezing and talking. The germs are fre- 

 quently there in considerable numbers before the affected per- 

 son is perceptibly ill, and they are often present in large 



