The prevention of intestinal putrefaction is, however, equally important in younger people. As Combe proves, we can avoid this by the use of certain kinds of food, especially carbohydrates and fruit, and by other substances producing lactic acid, which is, indeed, the best disinfectant for the intestines. The great benefit of various kinds of sour milk generally has been pointed out by Metschnikoff and his disciples. Among the causes of old age this savant attributes an important rôle to the processes of putrefaction in the intestines, and to avoid this he recommends the use of a certain kind of sour milk produced by fermentation by a number of microbes, including the Bulgarian _Bacillus maya_. That certain kinds of food exercise poisonous effects when introduced into the intestines is a matter of common observation. Thus, in not a few cases, fever, accompanied by cutaneous eruption, may be witnessed after partaking of strawberries or oysters, and especially after eating meats (notably sausages) which are in a state of decomposition. Severe cases of poisoning, even resulting in death, have occurred; and in Germany there have been, from time to time, regular epidemics after partaking of sausages in the above condition. Of course everyone partaking of such poisonous food will not become poisoned as this is prevented by the action of such glands as the thyroid and liver, whose function it is to preserve us from such effects. People in possession of healthy sensory organs,—eyes, nose, and tongue,—will be enabled to tell whether meat is in a fit condition to be eaten or not; but frequently we cannot discover by our senses a state of decomposition when such is not in an advanced stage, and if such food is taken regularly and in large quantities the great number of microbes we thus introduce into the intestines will poison us slowly but surely. Such poisonous microbes thrive and multiply very well in the alkaline contents of the intestines, but the growth of such dangerous bacteria can be greatly hindered by the introduction therein of acid substances, especially lactic acid. It has been observed by several authorities, such as Grundzach,[213] Schmitz,[214] and Singer,[215] that lactic acid decreases intestinal putrefaction, and also the conjugated ether sulphates in the urine. Footnote 213: Grundzach: Zeitschrift für klin. Medicine, p. 79, 1893. Footnote 214: Schmitz: Zeitschrift für Physiologische Chemie, vol. xix, 1897. Footnote 215: Singer: Therapeutische Monatshafte, p. 441, 1901.