IV. PHYSIOLOGICAL PROPERTIES OF THE "A" VITAMINE
Most authorities are now agreed that both the "A" and "B" types are essential to growth. Rohmann still holds out against the vitamine hypothesis. McCollum has recently pointed out that while rats do not have scurvy it does not at all follow that the absence of the "C" in their diet is immaterial, but that the contrary is true. Failure to grow, then, may manifest itself as a result of the absence of either of the first two types and possibly is affected by the absence of the "C." We have already seen how this failure may be utilized to measure the vitamine content of a source. The absence of the "A" type however may also manifest itself in another way, viz., by the development of an eye disease which McCollum first designated as xerophthalmia or dry eye and which the British authorities prefer to designate as keratomalacia. The failure of this result to always follow the absence of the "A" type in the diet has led some to question the specificity of this disease. While the infection of the eye is due to other agents the sum of the evidence supports McCollum and points to the absence of "A" as the true predisposing cause of the disease. Bulley, basing her claims on a study of some 500 rats fed on a synthetic diet, claims that the eye condition is not primarily due to a dietary deficiency but to an infection resulting from poor hygienic conditions. In reply to her contentions Emmett has reviewed his own data and presents them in the following summation:
_________________________________________________________________________ | | | | RAT | KIND OF VITAMINE | NUMBER CASES | POSITIVE CASES | PER CENT GROUPS | ABSENT IN THE RATION | REPORTED | OF XEROPH- | POSITIVE | | | THALMIA | _______|______________________|______________|________________|__________ | | | | A | Fat-soluble "A" | 122 | 120 | 98 B | Water-soluble "B" | 103 | 0 | 0 C | None | 216 | 0 | 0 _______|______________________|______________|________________|__________
In these groups special hygienic measures were taken against infection. Furthermore repeated attempts were made to transmit the eye disease by using sterile threads, passing them carefully over the edges of the sore lids and then carefully inoculating the eyes of other rats. These attempts resulted negatively in all cases where the inoculated rats had plenty of the "A" vitamine. Treatment of advanced cases of sore eyes with a saturated solution of boric acid and also with a silver protein solution failed to relieve the condition while as little as 2 per cent of an extract containing the "A" vitamine when added to the ration, speedily resulted in cure and increase of weight. These results combined with similar data compiled by Osborne and Mendel seem to refute Bulley's contentions and to justify our acceptance of xeropthalmia as a specific vitamine deficiency disease.