VARIATIONS. 305 



Variations of Pat in Different Churns. When milk is 

 divided into portions, as is the case when it has to be transported 

 by railway, considerable variations in fat are sometimes noticed. 

 As examples, the following analyses may be quoted : 



Series I. Series II. 



Seasonal Variations of Proteins with Solids not Pat. 

 In 1911, a year in which there was more than usual variation of 

 solids not fat according to season, the daily estimations of proteins 

 were averaged for each month, and it was found that the varia- 

 tions of solids not fat were chiefly due to variations in the proteins, 

 and it has been confirmed in other years that the low solids not 

 fat found in July and August are accompanied by slightly low 

 proteins. 



Seasonal and Monthly Variations. Distinct variations 

 according to season are found ; these will be shown by Table 

 LXV., which gives the mean monthly averages of milk for the 

 twenty years, 1897-1916. 



The year, roughly speaking, can be divided into four periods : 



(1) November, December, and January ; the milk is rich, both 

 in fat and solids not fat. 



(2) February, March, and April ; the solids not fat do not 

 show appreciable diminution, but the fat becomes less in 

 quantity. 



(3) May, June, July, and August ; the fat is low, though there 

 is a tendency to rise at the end of the period. In July and 

 August the solids not fat are below the average. 



(4) September and October ; an improvement in quality both 

 as regards fat and solids not fat is noticed. 



These periods correspond approximately to the seasons ; 

 winter milk is of very good quality, while summer milk is the 

 poorest ; the spring and autumn are transition periods. 



The quality varies in a ratio inverse to the quantity 

 yielded. 



In the analyses below (Table LXV.) the specific gravity has 

 always been determined by a lactometer ; the fat determinations 

 were made by the Gerber method. The total solids have been 

 calculated by the formula devised by the author. 



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