Mann (_Brit. Med. Journal_, 1908, V. II, p. 1673), expresses a similar opinion thus: "Most men if they choose to smoke can do so within certain limits without injury to health. Some men can exceed such limits with apparent impunity. The extent of the limitation must be determined by each man for himself." CHAPTER XVIII THE BENEFICIAL EFFECTS OF TOBACCO ITS DISINFECTING ACTION. PROTECTION AGAINST INFECTIOUS DISEASE. PSYCHOLOGICAL EFFECTS OF SMOKING. THE BENEFICIAL QUALITIES OF TOBACCO In the previous chapters the possible harmful effects of using tobacco have been dealt with at length. In this chapter we shall deal shortly with some positive beneficial effects. There is very little doubt that tobacco is a strongly protective agent against infection from disease. Its germicidal qualities are well-known and recognized. It is now recognized by medical writers that the mouth is one of the principal, if not the principal channel of infection for many infective diseases. The cavities of the teeth are the breeding places of hosts of pathogenic bacteria, of which there are about 100 different varieties arising from decaying food and other sources. These destructive agents, many of them highly pathogenic, easily find their way from the mouth through various channels to the inside of the body. Many infective organisms floating in the air are drawn into the mouth in the act of respiration and this is a common method of falling a victim to contagion. The effect of tobacco juice on the bacteria of the human mouth was investigated by Dr. W. D. Fullerton and is reported by him in the _Cleveland Med. Journal_ 1912, page 585.