160 ELEMENTS OF PHYSIOLOGY 



of plants, aided by the sunlight, are constantly removing 

 it, so that it is kept at .004 of one per cent in the air. If 

 it increases in the blood greatly beyond the usual amount, 

 dullness of mind and finally unconsciousness result. 



267. Foul Air. Besides the carbon dioxid, the air 

 coming from the lungs contains a small and variable quantity 

 of water and of foul-smelling vapors. In the air of a closed 

 room in which several persons have been for some time, 

 there is a characteristic odor which belongs to man, just as 

 there are odors peculiar to each of the lower animals. The 

 odors are caused by fine organic particles from the skin 

 and lungs of the persons. When a number of human 

 beings are together, and the ventilation is imperfect, the 

 air becomes very oppressive and is called " crowd poison." 

 Although it is given off by the cleanliest and healthiest 

 persons, the " crowd poison " accumulates faster if indi- 

 viduals in the room ( whether it be church, school, parlor, 

 or theater ) have catarrh, decayed teeth, or some other 

 diseased condition. The necessity for breathing and ven- 

 tilation is just as great, because of these organic particles, 

 as it is for the purpose of preserving the proper propor- 

 tion of inorganic elements in the air. Headaches and 

 other symptoms of distress, caused by ill-ventilated rooms, 

 are to be attributed chiefly to the effects of the " crowd 

 poison " upon the nerves. 



268. THOUGHT LESSON. Protective Instincts: Effects 

 of Tobacco on Lungs and Habits of Life. i . Chemical 

 analysis shows that there is enough nicotine in one cigar 

 if taken into the system, to kill two men. Does the expe- 

 rience of tobacco users disprove this ? 



2. Name, in four words, four disagreeable effects that 

 soon follow smoking a pipe or strong cigar for the first 

 time. 



3. Name two qualities belonging to tobacco that God 

 has given it in order to teach us through the senses that 



