LENTICULAR CATARACT 187 



divisions, the inhibitory factor fell not into the nerve 

 cells of the auditory centre, but into those of the cerebral 

 cortex, inducing inhibition either of development or of 

 phj'siological activity of those nerve cells which give us 

 our intelligence, then the individual would be not deaf, 

 but an idiot, a lunatic, or a mental defective, or would 

 manifest some other form of mental degeneracy. But 

 suppose further that it fell not into either of these groups 

 of nerve cells, but into the connective tissue cells of the 

 retinal epithelium, then we should have retinitis 

 pigmentosa.* 



Of this disease, of cataract, of deafness due to nervous 

 lesions, and of insanity a general proposition may be 

 made. The existence of some definite chemical compound 

 can be conceived as setting up the specific changes in 

 the various tissues concerned. We know that locomotor 

 ataxy is due to degenerations of the nerve tissues 

 of the spinal cord and is followed by an over- 

 growth of connective tissue, set up by the specific 

 poison produced from the body fluids by the 

 presence of the sj^philis spirochaete. There is nothing 

 improbable in supposing that the overgrowth of the 

 connective tissue of the retina, by which its percep- 

 tive nerve cells become disorganised, is similarly produced 

 by the formation of some subtle chemical compound. 

 The elemental factors of this compound may be 

 introduced separately by the parental gametes. If the 

 gametes of one parent carry onlj^ one factor of the com- 

 pound and the gametes of the other parent are normal, 

 that is, carries none of the factors, then the individual 

 born of such parents will be apparently quite normal 

 as regards this disease, yet all the while carrying one of 

 the pathological factors which in union with the com- 

 plementary factors will result in a manifestation of the 

 disease. But if this apparently normal person marries 

 another apparently normal person whose gametes, 

 however, carry the complemental factor or factors, 



* Of course in this case, the factor need not be an inhibiting factor, it 

 might be an exciting factor stimulating overgrowth of the retmal tissue. 

 Or we may suppose that the natural gro^^th of connective tissue is itself 

 inhibited under normal circumstances, at an appropriate time. In this 

 case the factor causing retinitis pigmentosa may be an inhibiting factor 

 which inhibits the normal inhibiting factor of growth. 



