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*.- SECT.*XVIIL. PHYSIOLOGY. 155 
support their contraction in a salubrious state. 
Besides spicy aliment, the Asiatic Indians chew 
the nut of the Mimosa Catechu, and the leaves of 
the Piper Betel powdered with chalk, which keep 
up the salutary action of the bowels. But spices, 
which are beneficial in the torrid zone, are for the 
most part injurious or superfluous in cold coun- 
tries, where the distribution of the blood is ade- 
quate to maintain the healthy irritability of the 
bowels. | 
cccLxxxIV. Before quitting this subject, it may 
not be irrelevant to notice the manner in which 
the alimentary canal is closed at its termination. 
cccLxxxvVv. The end of the rectum is surrounded 
by numerous spongy fibres, interwoven with each 
other, which in a healthy state are always in a 
state of expansion that is only overcome by me- 
chanical force: by this mechanism, the rectum is 
firmly and constantly shut, and the egress of feecal 
matter prevented. When the pressure of the 
feeces is on the point of overcoming the expansi- 
bility of this spongy texture, it becomes necessary 
either to expel them, or to contract the sphincter 
and levator ani, which are completely at the com- 
mand of the will. The expansibility of this 
fibrous tissue is sometimes destroyed in hemiplegia, 
and when this is the case, it forms a most dis- 
tressing part of the disease. 
