186 MEDICINAL AND POISONOUS PLANTS 
amount by persons of mature years, tobacco is always in- 
jurious, is a question with regard to which medical opinion 
is divided. All competent observers, however, are agreed 
that unrestrained use invites serious ills, produces enfeebled 
digestion, heart disease, and nervous debility, and may lead 
to insanity. Furthermore, all are agreed that even in very 
small amount, tobacco in whatever form is decidedly in- 
jurious to young persons, and that habitual use of it may 
quite unfit them for happy, vigorous life. It is a significant 
fact that those who are in training for athletic contests are 
forbidden to use tobacco. 
The drug coca consists of the dried leaves of the coca shrub 
(Fig. 174). These leaves mixed with ashes or lime are chewed 
extensively by the Indians of western South America as a 
means of lessening the sense of hunger and fatigue. Moderate 
use by the native mountaineers seems not to injure them, 
but excessive use produces effects as bad as those following 
the abuse of opium. Foreigners are found to be especially 
susceptible to the injurious properties of coca; and although 
with us it is widely used as a medicine, it must be regarded, 
like opium, as an especially dangerous drug never to be taken 
except on advice of one’s physician. The effect of coca upon 
the nervous system appears to be due partly to some volatile 
substance not yet satisfactorily determined, and to an alka- 
loid known as cocaine (C,;H.,NO,). This alkaloid has the 
remarkable property of producing insensibility to pain within 
certain restricted regions of the body to which it may be 
applied. Thus a small amount of a weak solution dropped 
upon the eyeball permits a a surgeon to operate upon thes 
organ without causing the slightest pain. 
Atropine (C,,H,,NO;) is another poisonous alkaloid of im- 
portant use. in connection with the eye. An exceedingly 
minute quantity locally applied causes the pupil of the eye 
to enlarge, by relaxation of the surrounding muscles, and 
thus makes possible an examination of internal parts which 
are ordinarily invisible. The alkaloid is obtained from the 
leaves and roots of belladonna (Fig. 175) a very poisonous 
plant. 
Quinine (C,,H.,N,O,) is one of many alkaloids obtained 
