While these results indicate that a fat deficiency may be withstood for a comparatively long period without obvious injury especially in early infancy, it may still be contended that prolonged feeding on such diets may be responsible for the onset of the disease in question.

That the fats themselves are not the influential factor is indicated by the cases referred to in which the disease developed on a diet containing a moderate amount at least of margarine, and finds confirmation in the work of Osborne and Mendel14 in which they demonstrated that rats could be maintained in excellent nutritive condition over considerable periods of time on diets practically free from fata provided they were supplied with adequate amounts of the vitamin A.15 If A is lacking in the ration on the other hand, the disease almost invariably makes its appearance among rats, even though the diet be amply supplied with fats such as lard and cotton seed oil.16

12 Von Grder, Bioch. Z. 07, 311, 1010.

13 Hess, Proc. Am. Soc. Biol. Chem., J. Biol. Chem. 41, xxxii, 1020.

14 Osborne and Mendel, J. Biol. Chem. 46, 145, 1020.

While there is general agreement as to the close connection of this disease with deficiency of A, there is some difference of opinion as to whether the eye-trouble is the direct outcome of the deficiency or is an infection which is successfully resisted by the normal animal but which develops and spreads rapidly when the resistance is lowered by malnutrition. Hopkins and Chick17 state that animals deprived of A become highly susceptible to bacterial infection.

In the case of rats they note that this lowered resistance first becomes apparent in many cases by the appearance of a characteristic infection of the external eye, which has been provisionally classified as a xerophthalmia. Osborne and Mendel18 remark: "Another type of nutritive deficiency exemplified in a form of infectious eye-disease prevalent in animals inapproprately fed is speedily alleviated by the introduction of butter-fat into the experimental rations.11

Hess, McCann and Pappenheimerl8a carried out some tests involving feeding young rats a diet markedly deficient in fat-soluble A. The diet consisted of casein, rice starch, salt mixture and, as fatty material, Crisco was used. In one case yeast also was administered and in another series of tests the animals were fed orange juice. A control set of rats received the same diet except a portion of the Crisco was replaced by 6% of butter-fat. They found that young rats receiving the diet, complete except for lack of fat-soluble A, invariably failed to grow and generally developed keratitis.

Bulley19 kept about 500 young rats on experimental diets for over a year, 50 per cent having an adequate amount of A, and the remainder on diets in which A was either deficient or absent (as shown by failure to grow). All were given fat-free alcoholic extract of yeast preparation as a source of B. During the whole period only five cases of xerophthalmia developed, of which two occurred on a diet which contained a limited supply of A; one occurred on a diet in which there was presumably sufficient A; one on a diet in which there was no A; and one on the ample stock diet. Two of the animals were growing well at the time, one remained with weight unchanged, and one lost weight. Each experiment lasted three or four months, and in each at least eight other rats were used which showed no sign of xerophthalmia. Bulley also reports unpublished experiments carried on by Totani, who kept rats for many weeks on a diet of extracted starch, extracted casein, sugar, lard, and the artificial salt mixture of Osborne and Mendel, without any signs of xerophthalmia, although Hopkins had previously found that this identical diet brought about typical xerophthalmia within fourteen days.

Bulley believes therefore that xerophthalmia is an infection, and that improvement on addition of A to the diet is simply the result of general improvement in health.

15 See also Drommond, Bioch. J. 13, 05, 1910.

16 Goldschmidt, Arch. f. Ophth. 90, 354, 1015; Freise, Goldschmidt, and Frank, Monatechr. f. Kinderh. 13, 424, 1015; Halliburton and Drummond, J. Physiol. 51, 235, 1017; Steenbock, Bontwell, and Kent, J. Biol. Chem. 35, 517, 1018; Steenbock and Gross, 26, 40, 501, 1010; Steenbock and Bontwell, lb., 41, 163, 1020; 42, 131, 1020; Steenbock, Sci. 50, 352, 1010; Emmctt and Stur-tevant, 8ci. 52, 300, 1020.

17 Hopkins and Chick, Rep. 38, Med. Res. Com. p. 17.

18 Osborne and Mendel, J. Biol. Chem. 16, 431, 1013.

18a Hess, McCann and Pappenheimer, J. Biol. Chem. 47, 395, 1021.

19 Bulley, Bioch. J. 13, 103, 1010.

Stephenson and Clark 20 ascribe Bulley's results to lack of sufficient purification of the basal diet. They found that among 46 rats, on a diet deficient in A, 28 per cent developed the typical eye-trouble, which was cured in every case by administration of A.

Against the theory of infection is the fact that the disease cannot be transmitted from one animal to another.21 Moreover, although absence of any one of the essential factors from the diet results in malnutrition, the xerophthalmia referred to is generally regarded as specific to deficiency of A. Steenbock22 states that an indistinguishable form sometimes occurs in animals on other rations,23 a theory which would serve to explain the observations of Funk and Macallum. These observers24 found that rats fed on a yeast and butter diet often exhibit the eye affections regarded by most investigators as characteristic of dietary deficiencies. Macallum25 noted that the substitution of moist brewers yeast for the dried form relieved the eye trouble to such an extent that it could be easily controlled by the use of dilute sulphate solutions, and Funk and Dubin26 have reported that out of 30 rats on artificial diets only one developed keratomalacia, and this was one which was getting five per cent of cod liver oil in the ration.

In this case the eye condition was cured by the administration of about 2 cc. of autolyaed yeast per day.

20 Stevenson and Clark, Bioch. J. 14, 502, 1920.

21 Bmmett, Sci. 52, 157, 1920; Nelson and Lamb, lb., 566; Am. J. Physiol. 51, 530, 1020.

22 Steenbock, Sci. Mo. 7, 179, 1918.

23 See also Steenbock and Bout well, J. Biol. Chem. 41, 90, 1920; Bulley, Bioch. J. 13, 103, 1919.

24 Funk and Macallum, J. Biol. Chem. 27, 51, 1916.

25 Macallum, Tr. Roy. Can. Instit, 1919, p. 175. 26 Funk and Dubin, Sci. 52, 448, 1920.