72 MASS. EXPERIMENT STATION BULLETIN 369 



concern the digestion of lactose. Sodium gluconate, fed ai conesponding levels, 

 exerted a similai, but rather more severe, deleterious effect. It would seem that 

 the gluconate radical in some way inhibits lactase activity. The phenomenon 

 known as "competitive inhibition of enzyme action" is postulated as a possible 

 explanation for this finding. A paper on this subject was published in Journal 

 of Nutrition 18:319, 1939 (Contribution 347.) 



A continuation of this work using both alpha- and beta-lactose fed at a some- 

 what lower level, 45 instead of 60 percent, confirmed the above findings in general 

 and gave no evidence of any dilTerence in the two forms of lactose. 



3. The Influence of Different Salt Mixtures on the Utilization of Lactose. 

 Preliminary evidence indicates that the amount and type of mineral elements in a 

 ration may influence the rate of breakdown and absorption of lactose. Two com- 

 monly used salt mixtures seem to have slightly different effects. Experiments 

 now in progress are designed to study the effect of the type and amount of salt 

 mixture on the growth, blood sugar, diarrhea, and lenticular changes of rats 

 fed a 60 percent lactose ration. 



The Comparative Effects of Kelp, Kelp-ash, and a Synthetic Salt Mixture on 

 Cholesterol-induced Atherosclerosis in Rabbits. (H. S. Mitchell and G. J. 

 Hadro.) A review of the literature shows a growing interest during the last 

 few yeais in the etiology and therapy of atherosclerosis. A disease similar to 

 that in humans may be induced in labbits by feeding cholesterol. By this device 

 factors which inhibit this pathologic change may be studied. Since a certain 

 degree of protective action by kelp was shown in previous experiments, it seemed 

 desirable to continue the investigation in an effort to ascertain, if possible, the 

 active principle in the kelp. 



In the preliminary experiment one litter confirmed the protective action of 

 the kelp while the other three were less positive in results. The observed correla- 

 tion between the amount of cholesterol eaten and the degree of lesions necessitated 

 more careful control of cholesterol feeding in subsequent experiments. Another 

 experiment was pei formed in which kelp, kelp-ash, and a synthetic salt mixture 

 prepared to resemble as nearly as possible the inorganic constituents of kelp 

 were fed to compare the effects of the whole kelp and inorganic constituents of 

 the kelp. About two-thirds of the iodine of the kelp was lost upon ashing. The 

 iodine content of the salt mixture was planned to correlate with that of the kelp. 



The salt mixture tended to inhibit hypercholesteremia and protect against 

 aortic lesions as well as the dry kelp and significantly better than the kelp-ash. 

 This indication that no organic factor in kelp is responsible for its beneficial 

 action and previous negative results with potassium iodide alone raise the ques- 

 tion as to whether some combination of inorganic elements including iodine is 

 responsible for protection of rabbits against cholesterol-induced atherosclerosis. 



The Adaptometer as an Instrument for Detecting Vitamin A Deficiency. (H. S. 



Mitchell, O. A. Merriam, and E. Miller.) It is generally accepted that vitamin A 

 is necessary for the synthesis of visual purple in the retina. Bright light bleaches 

 visual purple, which is resynthesized when a person adjusts himself to dull light. 

 The rate of adjustment is supposed to correlate with the amount of vitamin A 

 available up to a point of physiological optimum which has not as yet been 

 established. The Adaptometer was designed by J. B. Feldman for making rapid 

 dark adaptation tests on large numbers of persons in order to detect those show- 

 ing a marked deficiency in this respect. The American Optical Company, who 

 are manufacturing the instrument, provided a research grant to this depart- 

 ment for a survey of faculty and students on the campus, and for a study of the 

 limits of accuracy and usefulness of the instrument. 



