On returning to basal diet the rise continued till they reached about 95 grm., and for five weeks after the special diet ceased their weights were maintained at about the 90 grm. level. Then eye troubles recurred. One died and the other was used for preliminary experi-ments on another substance. The growth curves of this and of the other experiments are shown on Charts 1 and 2.

Experiment 2: A buck rat (Ad. 2, No. 1) of the same litter developed marked photophobia with loss of weight ten weeks after weaning. His brother, on the same diet, had died with marked eye symptoms about the eighth week. He was given a diet containing the whole fat obtained by percolation from the same weight of oyster as was used to make up the diet used in Exp. 1. The method adopted here was to mix the fresh oyster mince with sufficient Plaster of Paris to make it set hard in about 24 hours; the mass was then broken up finely and placed in an inverted glass bottle from which the bottom had been removed. Ether was allowed to pass down through the powder and escape with the dissolved fat from the neck which was provided with a cork and tube. Percolation was continued for one or two days till no more colour appeared in the ether. The ether was removed by distillation and the residue used for the diet. Immediate improvement set in, but the gain in weight was not maximal and was less prolonged than in Exp. 1. But it gave clear proof that the percolation method had extracted some of the vitamin. The amount of percolated fat consumed per day would be about 0.1 grm.

Experiment 3: Some of the same oyster material (June lot) was dried in a regulated oven at 52° C. for two days. The “fat” was extracted by the Soxhlet method, and both fat and residue made into diets similar to those used in Exp. 1 except that in one diet the “fat” replaced a corresponding amount of “Crisco,” and in the other diet the “residue” replaced a certain calculated amount of protein, carbo-hydrate, etc. These diets were given in succession to a doe rat (Ac, 2, No. 2). She was one of a group of three sisters; two had developed eye symptoms and had died 7 and 8 weeks after weaning. The survivor at 9 weeks had ceased to grow, and the eyes were apparently beginning to be affected. She was first given a diet containing Soxhlet fat. Little or no improvement resulted in the 12 days during which she received the diet, but on changing it to the “residue” diet a distinct increase was obtained.

Unfortunately, as stated already, this batch of June oysters was not so rich in vitamin-A as had been expected, and the level of intake of vitamin in these three experiments was low, but Experiment 3 shows that in the process of drying the vitamin becomes less soluble in ether—so that now the residue contains more vitamin than the extracted fat.

Experiment 4: On August 11 another quantity of oysters was obtained. Some of the material was dried overnight in the oven and extracted with ether (Soxhlet method). The “fat” and “residue” were then combined in one diet corresponding in general composition to basal diet, the object being to see whether material so treated could give a maximal effect. The amount of oyster used was much greater than what was used in Exps. 1—3, and was probably much more than was necessary. Two bucks (Ah, 3 Nos. 1 and 2) developed eye

symptoms and began to lose weight 8 weeks after weaning. On administering the oyster diet an immediate rise in weight set in, and within a week no trace of eye trouble could be detected. The diet was continued for 10 days, but on returning to the basal diet the beneficial result remained for 7 weeks; then one developed a lump in the neck and both had recurrence of eye symptoms and loss of weight. No. 1 died at 9 weeks and No. 2 at 11 weeks after the oyster diet had been discontinued. The amount of oyster per rat per day may be stated thus:—342 grm. fresh oyster yielded 6.72 grm. fat (1.96 per cent.) and 58 grm. residue (probably not quite water-free). These were made up into a diet containing about 214 grm. solids—the pro-portion of proteins was probably a little higher than the 20 per cent. usually present in basal diet. When the amount of water used in making up the diet is taken into account the amount of fresh oyster per day works out at 10 to 12 grm. on the assumption that the rat ate 10 grm. of the diet per day.

Experiment 5 and 6: A third quantity of oysters was obtained on October 12. They were in two lots; some were considered edible by the fishmonger, and others, spawning, would not have been sold in the ordinary course of events. These were larger oysters than the June ones (the August samples were not counted and weighed). The average weight of the unspawned was 10 grm., that of the spawn-ing, 8 grm. 200 grm. of each kind was made into a diet corresponding to the basal diet in the proportions of protein, etc.

Experiment 5: The rats in this case were offered a certain amount of the diet (3 grm. for the two) corresponding to 1 grm. of fresh non-spawning oyster for each rat in a separate dish. Along with this they received basal diet. Usually the oyster diet was eaten greedily, and was no doubt supplemented by the basal diet. The previous history of the two rats (Ah, 4, 2 and 3) was practically the same as the others of this litter (e. g. Ah, 3). Immediately after beginning the diet their weight rose rapidly, and the eye symptoms gradually disappeared. The diet was continued for three weeks during which the weights increased from 100 grm. to 150 grm. and from 70 grm. to 110 grm. After stopping the diet one continued to grow for six weeks, and reached a weight of 173 grm., the other remained at about 110 grm. for a slightly longer time. At the time of writing both are losing weight steadily and both have eye symptoms. This is the best result obtained with oysters so far, and is a clear proof that the vitamin-A content was high in this batch of oysters: for the 1 grm. of fresh material would not contain more than 0.25 grm. solids and the fat would not be more than 30 milligrm.

Experiment 6: The “spawning” oyster material was similarly prepared and administered in a separate dish to a doe (Ah 2, No. 2), but the diet when made was less concentrated than the other and in order to obtain the same amount of oyster the rat had to eat a larger quantity, viz., 3 grm. She was offered 7 grm. daily because at the time of commencing the diet it was uncertain how much would be required for either group. Almost from the first dose of oyster diet her weight began to rise, and it continued to rise rapidly in the three weeks during which the diet was given; she did not always consume the full ration of oyster diet. About three weeks after the return to