Shhehy — Average Percentage of Fat in a Cow's Milk. 551 



The graphs clearly demonstrate that an estimate of fat percentage made 

 from a few samples taken at random can seldom be correct. Thus in the case 

 of cow 97 readings from the crests of the graph of fat percentage would give 

 over 5 per cent, fat, while readings from the troughs would give less than 

 21- per cent. fat. The case of cow 128 is similar, but the difference between 

 the extremes is less marked. The mean fat percentage for each cow during 

 the investigation period may be represented by a smooth line drawn across 

 the irregular curves which join the actual daily fat percentages. The 

 frequent diversion of the irregular curve outside this average line is very 

 considerable in the case of most of the experimental cows. The following 

 table gives the recorded maximum diversions outside the mean for a period of 

 twenty days extending equally on either side of the date on which the 

 diversion occurs : the noticeable disturbance of the first week of July being 

 excluded :— 



Since the results obtained from the fat percentage in a number of random 

 samples are not satisfactory, it was thought that a better result would be 

 obtained by determining the total fat in a number of random samples. A 

 glance at diagrams If and III immediately disproves the truth of this 

 supposition, because the total fat shows variations at least as great as, if not 

 greater than, the percentage fat. In these diagrams the perpendicular scale 

 is such that in the three curves similar ascents and descents, that is, similar 

 lengths of line on the graphs, approximately represent similar variations. This 

 observation regarding total fat might have been inferred from the figures of 



