Chap. VI. WEEPIXG. 169 



the affection of the lacrymal glands through irritation 

 of the surface of the eye, it may be worth remarking 

 that, as soon as some primordial form became semi- 

 terrestrial in its habits, and was liable to get particles 

 of dust into its eyes, if these were not washed out they 

 would cause much irritation; and on the principle of 

 the radiation of nerve-force to adjoining nerve-cells, the 

 lacrymal glands would be stimulated to secretion. As 

 this would often recur, and as nerve-force readily passes 

 along accustomed channels, a slight irritation would 

 ultimately suffice to cause a free secretion of tears. 



As soon as by this, or by some other means, a reflex 

 action of this nature had been established and rendered 

 easy, other stimulants applied to the surface of the eye 

 — such as a cold wind, slow inflammatory action, or a 

 blow on the eyelids — would cause a copious secretion 

 of tears, as we know to be the case. The glands are also 

 excited into action through the irritation of adjoining 

 parts. Thus when the nostrils are irritated by pungent 

 vapours, though the eyelids may be kept firmly closed, 

 tears are copiously secreted; and this likewise follows 

 from a blow on the nose, for instance from a boxing- 

 glove. A stinging switch on the face produces, as I have 

 seen, the same effect. In these latter cases the secretion 

 of tears is an incidental result, and of no direct service. 

 As all these parts of the face, including the lacrymal 

 glands, are supplied with branches of the same nerve, 

 namely, the fifth, it is in some degree intelligible 

 that the effects of the excitement of any one branch 

 should spread to the nerve-cells or roots of the other 

 branches. 



The internal parts of the eye likewise act, under cer- 

 tain conditions, in a reflex manner on the lacrymal 

 glands. The following statements have been kindly 



communicated to me by Mr. Bowman; but the subject 

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