also, seem to furnish as good milk as those who are robust and strong. Age makes little difference, either, for the milk of women approaching the climateric has not been found inferior to that of mothers hardly out of their teens. The most striking fact about tht composition of milk, is its independence of outside influences. In fact, that a woman has a feeble child is no proof that the milk is at fault. On the contrary, it was found that the milk of women with feeble infants was rather richer than when the suckling was robust.

III. Influence of the mother's diet on the composition of her milk. Careful observations on this important subject were made by Baumm and Illner. They fed various nursing women on the following diets, and analyzed the milk produced from them:

I.

2.

An ordinary mixed diet taken in great quantities.

A highly nitrogenous diet-i. e., one containing much cheese and meat.

A diet rich in carbo-hydrates and fats, but poor in nitrogen, i. e., bread, sugar, butter.

3.

4.

A very fluid diet.

5.

An ordinary diet with 2 or 3 pints of beer daily.

6. A diet consisting largely of salt fish, pickles and other salt

foods.

They found that, on the whole, fat was the only ingredient of the milk on which the diet produced any appreciable effect. It was increased, sometimes rising 1% on diets one and two only. An abundant supply of carbo-hydrates had no influence upon the amount of fat. Nor, curiously enough, had the amount of fat consumed in the food; indeed, an increased amount of fat eaten seems to diminish rather than increase the amount of cream in the milk. These results are in harmony with those obtained in the feeding of cows, where a bean diet produces more and richer milk than any other, and the amount of fat is without effect. It is surprising, too, that an increased amount of fluid in the diet does not appreciably increase the total yield of milk. Nor did the diet of salted foods affect the composition of milk or the health of the child.

On the whole, the results of these and similar experiments tend to show that the composition of milk yielded is to a large extent independent of the diet, just as we have seen it to be of other external conditions. Even if the supply of food is to a large extent cut off, the mother goes on producing milk just as before, only at the expense of her own tissues. Thus, it was found that during the siege of Paris, women were able to continue nursing although almost starved to

death. The influence of alcohol on the secretion and composition of milk is a subject of great practical importance. The experiments just quoted showed that 2 to 3 pints of light beer daily had no effect on the composition of the milk, and other observers have shown that as much as 5 glasses of port or champagne are similarly devoid of influence.

Alcoholic liquors, then, cannot directly affect the quality of the milk. On the other hand, if a little bitter beer or a glass of wine at meals increases the mother's appetite and her power of digesting ordinary food, then such an addition to her diet will improve her own nutrition and with it the composition of her milk.

IV. Influence of frequency of suckling on the composition of the milk. The act of suckling serves as a stimulus to the breast, and if repeated at too short intervals, the richness of the milk is increased, and it may become less digestible. Hence, if a child is crying from indigestion, an attempt to quiet it by frequently giving it the breast is sure to lead to the production of an even less digestible milk, and so to an aggravation of the trouble.

One can arrive only indirectly at the amount of milk which a child should get at each meal and in the course of the day. Arguments from the size of the stomach in infancy are not of much value, for the individual variations in the size of the stomach are very wide, and the size after death is not a very certain criterion of the capacity during life. Nor is the amount of milk in the breast a certain guide, for the child need not exhaust the breast at every meal. A method which has been widely adopted is that of carefully weighing the child before and after each meal. If carried out on a sufficiently large number of infants, this method affords a fairly reliable basis from which to arrive at the average quantities required at each age. Obviously the data must only be regarded as affording average indications. They must not be applied too absolutely to any given child, for small and weakly children will require less nutriment than those which are heavy and strong, and healthy infants of a few weeks may take as much milk as feebler ones of as many months.

The importance of regularity in feeding cannot be exaggerated. By proper timing of the meals it can be arranged that the stomach. shall have plenty of time to empty itself, and thus one cause of indigestion will be avoided. The child is a creature of habit, and if it be trained to regular feeding hours will not expect food between meals.

Stomach digestion is not of much importance in infancy. The stomach in early life is small in capacity and of but feeble muscular power, and seems to allow the food introduced into it to pass quickly on

into the intestine, where the essential work of digestion is carried on. Thus, it has been found, by washing out the stomachs of infants at varying intervals after feeding, that if 3 ounces of milk be taken at a meal, fully 34 of it has left the stomach after the lapse of two hours, and that in another 20 or 30 minutes the stomach is entirely empty.

Whether the milk really clots in the stomach in very early life is disputed, some writers contending that there is no rennet to be found in the stomach during the first month. Whether this be so or not is not of very much importance, for the clot formed by human milk is very much looser than that formed of cow's milk, and does not offer any serious difficulty to the stomach in its digestion.

The absorption of the constituents of human milk in the intestine of infants seems to be very complete. Proteid is said to be absorbed to the extent of 99%, fat to 97%, and the mineral salts to 90%, while the sugar enters the blood in its entirety.

Comparing the nutritive value of a given amount of human milk and an equal quantity of cow's milk the two yield practically the same amount of solid nutriment, but the fuel value of cow's milk is rather greater, owing to the large amount of fat which the latter contains. The difference is not great, however for 100 grms. of cow's milk yield 66 calories and a similar quantity of human milk 621⁄2 calories. Both in building material and in fuel value, therefore, human milk is a poorer fluid than the milk of the cow.

When the mother is unable or unwilling to nurse her child we must turn to some other source. Naturally the best substitute is a wet-nurse, but there are many objections to this plan, so cow's milk is chosen as the basis of the artificial food. The average quantitative difference between cow's milk and mother's milk is as follows:

One sees that the total amount of solids in the two kinds of milk is about the same, yet the relative proportions of the different constituents in the two cases are very difftrent. Cow's milk is the richer in proteid, mineral matter, and (to a less degree) in fat; human milk excells in sugar. The superiority of cow's milk in the building materials is no doubt due to the more rapid rate of growth of the calf than of the

infant, but the excess of carbo-hydrate in human milk is rather surprising when one compares the relative muscular activities of the calf and the baby. It suggests that some of the sugar in the human milk is intended as a weak form of fuel instead of the more powerful heat producing fat, and this substitution may be due to human milk having been devised as an infant food suited to a warmer climate than that civilized man now occupies.

On more closely examining cow's milk, the difference in kind between its principle ingredients and those of human milk are even greater than the differences in their relative amounts. Sugar is the only constituent which is identical in kind in the two milks; the nitrogenous matters, the fat and the mineral salts must be compared separately in each.

The proteids of milk are of two kinds, casein and albumin. Cow's milk contains relatively more of the former and human milk the latter. The exact proportion as given by analysis vary considerably, but a reliable estimate has given six parts of casein to one of albumin in cow's milk, and the proportion of the two in human milk is equal. Albumin is a much more easily digested form of proteid than casein, it is evident that here is an important practical difference between the two milks. Not only is this true but the casein itself is actually different in the two forms of milk. Cow's casein leaves behind an indigestible residue (paranuclein); human casein does not.

When an acid is added to cow's milk the casein is thrown down in large flocculi, which do not readily dissolve in excess; under similar treatment human milk yields very fine flocculi which readily go into solution on adding more acid. Lastly, human casein is richer in sulphur. For these reasons human casein is more easily digested.

The fat of human milk contains more oleic acid, and has consequently a lower melting point and is more easily digested than the fat in cow's milk. This greater digestibility of the fat of human milk is increased by the fact that it is present in a much finer state of division than the fat droplets in cow's milk.

The mineral salts in the two forms of milk show important differences. In its high proportion of organic phosphorus, human milk recalls the chemical peculiarities of plant embryos or the yolk of egg. Considering the great importance of phosphorus in the nutrition of the infant, and the fact that organic combinations of it are probably more easily assimilated than in its organic salts, one must admit that the differences between human and cow's milk just pointed out are not to be lightly disregarded.

It is a familiar fact that most young infants have much greater

difficulty in digesting cow's milk than that of their own mother. The chief reason for this is that cow's milk forms a much denser clot in the stomach than human milk. The greater density of the clot is due, first, to the absolutely larger proportion of casein in cow's milk, and probably also to those chemical differences in the casein already mentioned; second, to the smaller proportion of fat and soluble albumin relative to the casein which characterizes cow's milk-the soluble albumin and fat of human milk seem to act mechanically in producing a loose clot; third, to the fact that the cow's milk contains six times as much calcium and three times as much acid as human milk, and the density of the clot depends very much on the proportion of these two constituents. For all these reasons cow's milk tends to form a dense, retracted clot in the stomach, while the clot of human milk is loose, friable and easily broken up. In the intestine there is not so much difference between the two.

In most cases, especially in young infants, it will be found necessary to modify the milk in some manner. By suitable treatment, the proportion of casein, calcium and acid salts present can be reduced, and the digestibility of the milk duly raised.

The simplest method is by mere dilution. The problem here is to reduce the casein and mineral matters in the cow's milk, to leave the proportion of fat as it was, and at the same time to raise the amount of sugar. Taking the average composition of milk and adding one part of water to two parts of milk we get the proportion of proteid about right, but leave the fat 1%, and the sugar 32% too low. If now you add to every eight ounces, two teaspoonfuls of milk sugar and 1⁄2 ounce of cream (containing 15% of fat) these defects are rectified, and, except for a slight excess of mineral matter, the mixture will have approximately the same proportion of each ingredient as human milk. The digestibility of such a mixture is still inferior to that of milk from the breast, for water in this proportion does not prevent a dense clot in the stomach. For this reason it is better to dilute with lime water rather than with plain water, for lime water possesses a specific power of preventing the clotting of milk, even in the proportion of 1-3 of the whole mixture. In the case of very young or weakly infants, it may be necessary to dilute the milk more freely than in the proportion given above. In such a case a mixture of equal parts of milk, water, and lime water is to be recommended, cream and sugar being added as before. Although this is chemically weaker than milk many infants thrive upon it well enough. After a while use two parts of milk to one of water and one of lime water, and finally arrive at the stage where the water is left out altogether.