SECTIONAL TRANSACTIONS.— 1. 601 



relationships the united efforts of the agricultural chemist and physiologist are 

 necessary. Milk itself must be considered not only as a ready formed liquid, but as 

 a link between succeeding generations, in any stage of the formation of which the 

 true significance of these interrelationships may be sought. 



The extremely complicated component known as milk fat is, as it were, cut off 

 from its fellows by its physical condition in milk ; the relationships of its components 

 to other constituents must, therefore, be sought in earlier stages of the formation of 

 milk fat. Among these components, vitamin D, the antirachitic and calcifying 

 vitamin, is intimately connected, not only with the deposition of calcium in 

 the bones of the foetus, but later through the milk in the bones of the young 

 mammal. 



In a series of experiments conducted at the National Institute for Research in 

 Dairying, Reading, and extending over seven years and involving prolonged feeding 

 of over sixty cows in all, the milk was weighed and tested for fat at each milking 

 and the effect of various winter rations compared with and without the addition of 

 cod-liver oil as a concentrated source of fat soluble vitamins. In the earlier years 

 of these experiments, when the difference between vitamins A and D had not been 

 recognised, growth of rats fed on butter prepared from the milk of the experimental 

 cows was taken as a criterion of richness in fat soluble vitamin. In these earlier 

 experiments a tenfold difference was observed in the growth-promoting properties 

 of the butter produced from cows fed on a diet of concentrates, seeds, hay and mangels, 

 as compared with the butter from cows fed on a ration containing cod-liver oil or green 

 grass. That is to saj% that 0-1 gram of either of the latter was equivalent in this 

 respect to one gram of the former. 



Our subsequent experiments have confirmed these results and indicate that the 

 vitamin A and the vitamin D are derived from the food and that a good winter ration 

 for cows, containing silage and hay, may produce an antirachitic butter of moderate 

 potency. Doses of cod-liver oil above two ounces may improve the antirachitic 

 value of this butter. If, however, the control ration is composed of straw, mangels 

 and concentrates, the difference between the controls and the cod-liver oil fed cows 

 is much more marked in this respect. The vitamin A is also increased by feeding 

 kale in winter time, but without increasing the vitamin D. 



Experiments have also been carried out on the effect of this cod-liver oil feeding 

 on the other constituents of the milk and an increase in the percentage of total calcium 

 by feeding cod-liver oil has been demonstrated by Dr. Mattick in my laboratory. 



Turning to a review of the percentage composition of the milk as a whole, charts 

 illustrate the variation in the fat content and weight of milk of control cows in some 

 of the groups under experiment. The variations found in a study of the milk during 

 the lactation period revealed the fact that the nature of each cow in respect of milk 

 yield and fat is characteristic of the individual. It also appears that within the 

 limits of adequate nutrition diet has, as a rule, no direct permanent influence on the 

 percentage of fat in the milk. Even when the volume of the milk yield is increased 

 by previous management and feeding the percentage of fat seems to be unaltered 

 beyond the limits of variation due to other causes. 



It came as a surprise to find that when cod-liver oil was included in the diet of a 

 cow in excess of a certain amount the percentage of fat fell to a degree below the limits 

 of daily variation. 



Diagrams exhibit the effect in the 1925 experiments which occurred with four 

 ounces, and in the 1926 the depression was observed only when six ounces were given. 

 Last winter the depression was very slight and observed only when eight ounces were 

 given, and this spring a further series of experiments with oils from various sources 

 showed a varying depression of fat in some cases only. 



In other experiments the unsaponifiable fraction from the cod-liver oil was fed to 

 four cows but produced no depression. 



A study of the results indicate that it is not the oil itself which produces this 

 unusual and unexpected effect on the richness of cows' milk but a constituent which 

 varies in amount in different oils. The alterations which have taken place in the 

 preparation of cattle cod-liver oils during the seven years over which the experiments 

 have extended, may be responsible for the variations observed. 



This unexpected effect sometimes produced by cod-liver oil has been taken into 

 account in estimating the increase in vitamins produced in milk by feeding cod-liver 

 oil as a source of vitamins A and D. 



Whether or not the constituent of cod-liver oil which is responsible for the 



