THE MILK. 437 



a saturated solution of the salt, the nitrogen is then determined as 

 above. The result multiplied by 6.37 indicates the amount of 

 caseinogen. The amount of lactalbumin can be ascertained by 

 deducting the value found for caseinogen from the total amount of 

 albumin, or by diluting the filtrate, after separation of the casein, 

 precipitating with tannic acid, and determining the amount of nitro- 

 gen as before. In this case also we multiply by 6.37. 



The results for caseinogen thus obtained are not absolutely accurate, 

 as the globulin is likewise precipitated by magnesium sulphate. 

 Its amount, however, is so small that it may well be disregarded. 



The Fats. The fats which are found in the milk, viz., in butter, 

 are essentially the same as those which occur elsewhere in the 

 animal body, viz., stearin, palmitin, and olein. In addition, how- 

 ever, we also find small amounts of the triglycerides of myristinic 

 acid, butyric acid, and capronic acid, and traces of caprylic acid, 

 caprinic acid, laurinic acid, and arachinic acid. 



Stearin, palmitin, and olein constitute about 98 per cent, of the 

 total amount, and of these, olein represents about 29.4-39.2 per 

 cent. As a consequence of the large quantity of olein which is 

 thus present, the melting-point of butter is relatively low, viz., 

 31-34 C., while it solidifies between 19 and 24 C. 



In addition to the neutral fats, butter also contains about 7 per 

 cent, of volatile fatty acids, of which 3.75.1 per cent, are repre- 

 sented by butyric acid and 2-3.3 per cent, by capronic acid. 



Formic acid has been found in butter which had been exposed to 

 sunlight. 



Of the origin of the fats which are found in milk we know that 

 they are to a large extent derived from albumins, and I have already 

 pointed out that their amount increases with a diet that is rich in 

 such material, even though no fat is ingested at all. They diminish 

 materially if fat alone is ingested, and are not increased if much fat 

 is administered, while the ingestion of albumin remains constant. 

 They are probably formed in the gland directly, and on micro- 

 scopical examination it is possible to demonstrate their presence in 

 the cells, in the form of fine globules, which are soluble in ether, 

 and are colored black on treating with osmic acid. 



More recently Engel has shown that the sources of the milk fat 

 may not be found in the breaking down of the gland elements, but 

 that they are furnished by the body fat and the fat of the food. It 

 has been shown conclusively that the fat of the food enters the milk 

 fat and that feeding with fat increases the amount of fat in the milk, 

 but whether this can be done for a prolonged period of time is still 

 doubtful. Engel is of the opinion that the fat of the food enters 

 regularly into the secretion of the mammary gland. The colostral 

 fat seems to be, in the human species at least, constantly identical 

 with the body fat. 



To isolate the individual acids which enter into the composition 



