2 MILK AND ITS HYGIENIC RELATIONS 



considered. Subjects not directly connected with these aspects 

 have either been omitted or have been accorded only brief mention. 



It seemed desirable for the sake of clarity to give some 

 account of the general composition of the only two varieties of 

 milk which are used as a food in considerable quantity in this 

 country that is, human and cows' milk. 



It is hoped that the dreariness of the figures giving the average 

 composition of milk may have been slightly relieved by a dis- 

 cussion of the causes of variation in composition, known at present 

 rather to agriculturists than to hygienists. 



The chapters following that on the general composition of 

 milk contain, it is believed, material which has not hitherto found 

 its way into English text-books. The literature on the subjects 

 of these chapters has been given as completely as possible, and the 

 so-called ' Biological Properties ' have been dealt with fully. The 

 great and wholly unmerited importance which has frequently 

 been attached to some of these properties (e.g. the ferments), and 

 the general ignorance of the value to the young of the same species, 

 of certain other properties of colostrum, appeared to justify the 

 devotion to them of considerable space. 



After considering the composition of human and cows' milk as 

 fully as appeared to be necessary, it was decided to deal first with the 

 supply of human milk under the heading of breast-feeding. Until 

 recently much of the most useful knowledge upon this important 

 subject had been published in foreign literature. In direct sequence to 

 this subject comes the question of the nutritive value of the boiled 

 milk of the same species as a food for both infants and calves, and 

 this again leads directly to a consideration of the nutritive value of 

 the milk (raw and heated) of a foreign species, that is, to the arti- 

 ficial feeding of infants and young animals. 



The experimental data upon this important subject have been 

 fully dealt with, and opinions or statements unsupported by fact 

 have been excluded. 



Details as to the methods of infant feeding have been omitted 

 except for an occasional reference, since it is not only outside the 

 lines of this work, but also because precise data are so frequently 

 lacking in the papers upon this subject. 



It seemed impossible to ignore altogether the question of milk 

 production, and of commercial methods of treating milk. These 

 have, however, been dealt with as briefly as was felt to be consistent 

 with a clear presentment of the subject. 



The great variety of the branches of knowledge which it has 

 been necessary to bring under review render it almost impossible 

 for any one writer to be personally conversant with them all ; 

 this must inevitably lead to some unevenness of treatment, which 

 it is hoped may receive the indulgence of the reader. 



The book is intended to appeal both to the expert and to the 

 person without technical knowledge. In the endeavour to simplify 



