143 



increase the per cent of hard fats, while linseed meal, gluten feeds, succu- 

 lent pasture grasses, etc., are conducive to raising the per cent of soft fats. 

 It is by no means established, however, that the feed is the only nor even 

 the chief factor controlling the proportion of fats in milk. Thus at the 

 time when the soft fats increase in milk and butter produced in this sec- 

 tion of the country most of the cows are fresh, and it is quite possible 

 that the period of lactation exerts an important influence on the fats. 

 It was, therefore, deemed expedient to investigate in how far the period 

 of lactation does affect the fats in milk. 



Three cows of the university herd were selected and fed during their 

 respective periods of lactation on an uniform ration, evading such feeds 

 as would tend to materially influence the hard or soft fats. The milk 

 from each cow was separated, the cream ripened and churned separately, 

 and the butter analyzed for volatile, soft and hard fats. 



The generally accepted classification of milk fats is as follows : 



fi-l™>ririps nf / a - volatile or soluble fatty acids. 

 Uiycenaes ot j b insoluble fatty acids 



The glycerides of the insoluble fatty acids are subdivided into hard 

 and soft fats. The dairy literature, in dealing with the soft fats and 

 their relation to the melting point of butter, gives consideration to the 

 glycerides of the insoluble fatty acids alone. Inasmuch as the glycerides 

 of the volatile or soluble fatty acids have a very low melting point as 

 compared with that of insoluble fats, a comparatively slight change in 

 the per cent of the volatile fatty acids must greatly influence the hardness 

 or softness, as well as the melting point of butter. In determining the 

 variations of the soft fats in butter it is necessary, therefore, to take into 

 consideration the soluble as well as the insoluble fats. 



The following charts show the results of analyses of butter made 

 from the milk of the three cows under experiment: 



