Studies of starvation suggest the same thing. Various experiments have shown that in the later but premortal stage of starvation there is a certain activation of vital processes, including heat production, and it is possible that this has some significance for regeneration. Higher animals are apparently unable to use their own tissues as a source of nutrition to any such extent as the lower forms can do, and this is probably connected with a higher physiological stability of the tissue components. The body weight often does, however, increase and become greater after starvation than it was before, so that a fasting period is followed by an increase in vigor and body weight and hence the wide belief in its therapeutic value. On the other hand, the injurious effects of over-nutrition in man are supposed to be due to the accumulation of food or to intoxication, but it is possible that overnutrition actually increases the rate of senescence by augmenting in the cellular substratum not only the decomposition of food but other substances that decrease the rate of metabolism. There are certainly many instances of longevity in man on a low diet. Again, after certain bacterial diseases, for example, typhoid, the body weight often becomes greater and vigor increases. While low diet often does good, it may, on the other hand, aggravate many diseases. Frogs and salamanders may live a long time without food and undergo great reduction, and starvation sometimes has a directly rejuvenating effect. The animals grow much more rapidly afterward and use a larger percentage of nutrition in growth and attain a larger size than those continuously fed.