The Effect of Vitamine. Seven rats per set. Weight on the first day:

178 5 76

For four days both A and B were fed on the regular diet. At the end of the fourth day:

A 100 B 91

Both A and B were now placed on the "synthetic diet." On the 14 day:

A 121 B 111

To B's diet yeast was now added. A continued to grow until the 19 day. On that day the weights were:

A 129 B 121

Then for a number of days A remained stationary, showed a slight loss, and finally a small gain. In the meantime B continued to climb. On the 37 day the weights were:

A 134 B 171

B was once again placed on the "synthetic diet" alone. On the 53 day:

A 116 B 146

At this point yeast was added to A's diet. B remained on the synthetic. A's weight immediately began to jump. On the 82 day the weights were:

A 179 B 112

This, you will notice, is a variation of Professor Hopkins' classical experiment (see page 92). The principle is to add the vitamine-containing substance first to one group, and then to take it away from this group and add it to the other. The response, as the above experiment shows, is little short of marvelous.

General Conclusion

These experiments emphasize the importance of a mixed diet, such as control animals receive. Nature led us to select a mixed diet long before science could offer any explanation for such a preference; to-day our knowledge of the science of nutrition has reached the point where it can heartily endorse the value of a varied diet.