TROPHIC CENTRES AND NERVES. 645 



make any observations on the influence of the sympathetic upon the tem- 

 perature. 



Vaso- Inhibitory Nerves. There are certain nerves, the direct action of 

 which under Faradic stimulation is to dilate certain blood-vessels. These 

 nerves may also be excited by reflex action through the sensory nerves. In 

 many nerves, as the chorda tympani, the nervi erigentes etc., the existence 

 of inhibitory fibres has been demonstrated (Dastre and Morat, Eckhard, 

 Laffont, Vulpian and others). For example, division of the nervi erigentes 

 has no immediate effect on the penis, but Faradization of the peripheral 

 ends of the nerves dilates the blood-vessels and produces erection. Fibres 

 possessing this property undoubtedly exist throughout the body, in the sym- 

 pathetic and in the motor and mixed nerves ; and it is possible that there are 

 vaso-motor inhibitory centres, although such centres have not been located. 

 The mode of action of these nerves is analogous to that of the inhibitory 

 nerve of the heart, restraining and regulating the action of the vaso-motor 

 nerves and allowing the pressure of blood to dilate the vessels. It does 

 not, however seem proper to call them " vaso-dilator " nerves, any more than 

 it would be correct to call the inhibitory nerve of the heart the cardiac dilator 

 nerve. 



Trophic Centres and Nerves (so-called). Collections of nerve-cells act as 

 centres presiding over the nutrition of the nerve-fibres with which they are 

 connected ; but it has been found that the nutrition of certain parts may be 

 profoundly affected through the nervous system. Many pathologists, relying 

 upon the presence of certain lesions of cells in the cord, in connection with 

 cases of progressive muscular atrophy, admit the existence of trophic cells 

 and nerves. These views, however, rest almost entirely upon pathological 

 observations. Direct experiments upon the sympathetic in animals do not 

 positively show any influence upon nutrition, except as this system of nerves 

 affects the supply of blood to the parts. When a sympathetic nerve is 

 divided, there is an apparent exaggeration of the nutritive processes in par- 

 ticular parts, and there may be inflammatory phenomena, but atrophy of 

 muscles is not observed. Atrophy of muscles, indeed, follows division of 

 cerebro-spinal nerves only, or as cases of disease have shown, disorganization 

 of cells belonging to what are recognized as motor centres. As regards the 

 latter condition, there can be no doubt of the fact that progressive muscular 

 atrophy is attended with disorganization of certain of the motor cells of the 

 spinal cord. 



Without fully discussing this subject, which belongs to pathology, the 

 facts may be briefly stated as follows : There may be progressive atrophy of 

 certain muscles, uncomplicated with paralysis except in so far as there is 

 weakness of these muscles due to partial and progressive destruction of their 

 contractile elements. The only constant pathological condition in these cases, 

 aside from the changes in the muscular tissue, is destruction of certain cells in 

 the antero-lateral portions of the cord, with more or less atrophy of the corre- 

 sponding anterior roots of the nerves. It has never been assumed that there 

 are cells in the cord, presenting anatomical peculiarities by which they may be 



