474 



NUTRITION OF FARM ANIMALS 



also an increase of the total protein and of the total solids, 

 but these are relatively smaller than that of the fat, the totals 

 being 25 per cent and 21 per cent, respectively. There is also 

 an increase of 12 per cent in the proportion of ash, while the 

 lactose, on the contrary, shows comparatively small and ir- 

 regular changes, the extreme range of the differences being 

 ii per cent, while it does not increase regularly with the in- 

 crease of the other ingredients. The lactose is evidently the 

 most constant ingredient of the milk. 



565. Influence on composition of milk solids. The real 

 nature of the differences in composition, however, is rendered 

 clearer by computing the percentage composition of the water- 

 free total solids, with the results shown in Table 125 : 



TABLE 125. AVERAGE COMPOSITION OF MILK SOLIDS OF DIFFERENT 



BREEDS 



From the foregoing table, it appears that the percentages of 

 ash and of total protein in the milk solids are very constant, 

 the single figures differing but very slightly from the averages 

 of 5.36 and 26.10, respectively. The essential difference in 

 the composition of "the milk solids lies in the proportion of 

 lactose to fat, the former decreasing as the latter increases, 

 while the total percentage of the two taken together is prac- 

 tically constant, varying less than 0.7 per cent from the average 

 of 68.53 P er cent - In other words, it appears from these figures 

 that in cows producing milk rich in fat the secreting cells form 

 relatively less lactose and correspondingly more fat, while, as 



