792 THE REPRODUCTIVE ORGANS. [CH. LVII. 



There can, therefore, be but little doubt that we have to deal 

 with the trophic influence of nerves ; * but the dust, etc., which 

 falls on the cornea must be regarded as the exciting cause of the 

 ulceration. The division or disease of the nerve acts as the 

 predisposing cause. The eyeball is more than usually prone to 

 undergo inflammatory changes, with very small provocation. 



The same explanation holds in the case of the influence of the 

 vagi on the lungs. If both these nerves are divided, the animal 

 usually dies within a week or a fortnight from a form of 

 pneumonia called vagus pneumonia, in which gangrene of the 

 lung substance is a marked characteristic. Here the predisposing 

 cause is the division of the trophic fibres in the pneumogastric 

 nerves ; the exciting cause is the entrance of particles of food 

 into the air passages, which on account of the loss of sensation 

 in the larynx and neighbouring parts are not coughed up. 

 Another trophic disturbance that follows division of the vagi is 

 fatty degeneration of the heart. 



We shall conclude by giving x one more instance of trophic 

 disturbance due to nervous disease, and this is the case of bed- 

 sores. Many bed-sores are due to prolonged confinement in bed 

 with bad nursing ; these are of slow onset. But there is one 

 class of bed-sores which are acute ; these are especially met with 

 in cases of paralysis, due to disease of the spinal cord ; they 

 come on in three or four days after the onset of the paralysis in 

 spite of the most careful attention ; they cannot be explained by 

 vaso-motor disturbance, nor by loss of sensation ; there is, in 

 fact, no doubt they are of trophic origin ; the nutrition of the 

 skin is so greatly impaired that the mere contact of it with the 

 bed for a few days is sufficient to act as the exciting cause of 

 the sore. 



CHAPTER LVII. 



THE REPRODUCTIVE ORGANS. 



THE reproductive organs consist in the male of the two testes 

 which produce spermatozoa, and the ducts which lead from them, 

 and in the female of the two ovaries which produce ova, the 

 Fallopian tubes or oviducts, the uterus, and the vagina. 



* The proof, however, that there are distinct nerve-fibres anatomically is 

 not very conclusive. 



