THE CAUSATION OF DISEASE. 1 37 



or brood, are " similarly circumstanced in respect of incident 

 forces/' and therefore they must differ. Nevertheless, plants 

 grown from the seeds out of one pod, and animals produced at 

 one birth, are more like one another than plants grown 

 from the seeds of pods produced at different times, and anim,als 

 produced at different litters. The only remaining question is, 

 whether the differences in E are adequate to account for 

 the differences of the individuals? The fact that among 

 animals born at one birth, some may take after the father and 

 others after the mother, is an apparent argument against 

 the principle for which I am contending, but. one can well 

 understand how the nature of the E under which germ and 

 sperm spring into existence may so affect their delicate 

 structure as to strengthen or weaken, as the case may be, 

 the capacity of the one or the other to cause the offspring to 

 grow like the being from which it is derived. 



The remarkable likeness between human twins is nowhere 

 better shown than in the tendency which they display towards 

 the same diseases ; it proves that they are like one another, 

 not only in gross configuration, but also in the more delicate 

 structure of the tissues. I shall have occasion in another part 

 to speak of the pathological likeness of twins. Here I will 

 briefly mention two cases. A mother brought her twin babies 

 to me. Each of them was suffering from a syphilitic rash of 

 like character and distribution ; considering how varied are 

 the rashes met with in congenital syphilis, this likeness was 

 remarkable. The eruption appeared when the children were 

 three weeks old, in the one a few hours before the other. 

 Each child having developed under an almost identical E, not 

 only in respect of physiological conditions, but in respect also 

 of the specific mal-environment, what wonder that they should 

 exhibit this marvellous pathological likeness ! Again, I have, 

 the very day I write this, seen twin girls, of whom the mother 

 says : " They are always ill together ; the one never suffers 

 without the other." 



