306 THE HUMAN MECHANISM 



as a stimulant to the whole system in much the same 

 manner as do " smelling salts." 



It has been recently suggested that, owing to the incom- 

 plete character of the combustion, tobacco smoke contains 

 a small amount of the poisonous gas carbon monoxide (CO), 

 and it is quite possible that some effects of smoking 

 especially where the smoke is drawn into the lungs (inhaled) 

 may be attributed to this gas; but the suggestion has 

 not yet been submitted to the test of actual experiment. 



Indeed, the physiological action of tobacco probably not 

 only varies with the form in which the tobacco is used but 

 is in any case the result of a combination of a number of 

 factors partly physiological and partly psychical. We must 

 here, however, confine our attention to the purely hygienic 

 aspects of the matter. 



Human experience shows that the unwise use of tobacco 

 may unfavorably affect digestion, cause serious disorders of 

 the heart, and impair the work of the nervous system. Those 

 training for athletic events are usually forbidden the use of 

 tobacco because it " takes the wind " ; that is, makes impossi- 

 ble the most efficient training of the heart. Many employers 

 have found that youths who smoke cigarettes are less reliable 

 in their work ; and this is only one instance of the effect 

 upon the nervous system already referred to, the same result 

 being observed in a diminished steadiness of the hand, often 

 amounting to actual tremor. 



These effects do not, of course, manifest themselves in 

 their extreme form whenever tobacco is used, but it is 

 probable that they are always present in some degree. 

 Whether they are noticeable or not depends largely upon 

 the ability of the constitution to resist them. Tobacco is 

 thus often used without demonstrable bad effects when one 

 is leading a hygienic life ; but very often the habit, formed 

 under these conditions, persists after the increasing intensity 

 of occupation and the attendant cares and responsibilities 



