MILK AND CHILD MORTALITY 157 



Again there is a marked difference between the inci- 

 dence of this disease upon the babies of the rich and those of 

 the poor. The comparative immunity of the rich cannot be 

 adequately ascribed to boiling of the milk, since it is doubtful 

 if heating of the milk is practised much more extensively by 

 the well-to-do. The greater facilities for home infection at 

 the houses of the poor is a far more likely explanation. 



Also, as Ballard and many investigators have pointed out, 

 while the incidence of diarrhoea follows the earth temperature 

 it does not correspond with that of the air temperature. As 

 Sandilands l clearly points out, commenting upon this, the 

 number of germs in milk is largely a question of temperature, 

 and the higher the temperature of the air the more germs 

 in the milk supply at that given time. Since the diarrhoea 

 does not occur until some time after the onset of the hot 

 weather it results that, during hot weather at the beginning 

 or end of the summer, cows' milk containing enormous 

 numbers of bacteria may be consumed with comparative 

 impunity, and the incidence of diarrhoea is not directly in- 

 fluenced by the number of bacteria occurring in cows' milk. 



A further fact is that a small proportion (under 10 per 

 cent) of breast-fed infants get diarrhoea. Here the infection 

 must be other than by cows' milk and must be due to domestic 

 infection. 



It is probable that infantile diarrhoea is an infectious 

 disease due to one specific micro-organism, and that it is 

 infectious from case to case. Further, the actual place of 

 infection is usually domestic, and does not originate with 

 manurial pollution at the farm ; but this may not be true of 

 all cases. 



Most medical officers and others who have had experience 



1 Journ. of Hygiene, 1906, vi. 77. 



