154 ON VARIABILITY AND ADAPTATION 



other idioplasm or the constitution of the same is adequate to 

 counteract the loss of side-chains in the idioplasm of the mutilated 

 individual, there may be no recognizable effect. Or, on the other 

 hand, the effect upon this latter idioplasm may be so serious 

 as to lead to inherited defects in the offspring. But clearly 

 these defects will be of a different order and a more generalized 

 type ; they will not be identical with the mutilation. There 

 will be no direct transmission of acquired defects of this nature. 



2. The Indirect Transmission of Acquired Diathesis. — With 

 reference to diathesis, this also may be laid down, that acquired 

 disease, and the effects caused by disease, cannot in general 

 be transmitted in such a way that the offspring presents lesions 

 identical with those produced in the parent, though it has to be 

 recognized that there is the possibility of modification in that 

 offspring due to the parental disease. There is the possibility 

 of a certain amount of transmission, not of the identical local 

 lesion caused by the disease in the parent, but of a modified or 

 impaired condition of the germ plasm. We must recognize 

 that constitutional disease, by leading to disturbance in the 

 activity of important organs, tells not only directly upon these 

 organs, but secondarily upon other organs. It leads, for example, 

 to an altered condition of the blood, and so to altered nutrition 

 of all the cells of the body. Among other cells, the germ cells 

 may be directly affected, their idioplasm modified, and the off- 

 spring directly influenced. Conditions affecting the parents 

 are capable of influencing and modifying the descendants. It 

 is this which is forcibly brought home to us in our medical work. 

 It is changes of this order which are almost inevitably neglected 

 by morphologists. for they are not within their ken. The 

 changes brought about in the tissues by what is essentially 

 chronic intoxication may be so slight as to be inappreciable. 

 Microscopical examination may reveal nothing ; only by their 

 physiological effects can their existence be recognized. It is in 

 the study of these conditions and their effects that medicine 

 can afford the most valuable aid in the matter of inheritance. 



All infectious diseases are intoxications. If a parent is the 

 victim of syphilis, it is obvious from febrile and other phenomena 

 not merely that there are local toxic phenomena at the foci of 

 growth with multiplication of the germs of the disease, but that 

 the toxines pass into the general circulation. They may produce 



