CLASSIFICATION OF VARIATIONS 87 



present in all its germ-cells, male and female, taking part in their 

 symmetrical divisions, and passed on equally to all as much as 

 is the protoplasm or any other attribute of the breed. From the 

 body of the bird the critical and efficient substance could in all 

 likelihood be isolated by suitable means, just as the glycogen 

 of the liver can be. But even when this extraction has been 

 accomplished and the reducing body isolated, we shall know no 

 more than we did before respecting the mode by which the power 

 to produce it was conferred on the fowl, any more than we know 

 how the walls of its blood-vessels acquired the power to form a 

 fibrin-ferment. 



It is when the scope of such considerations as this are fully 

 grasped that we realise the fatuousness of the conventional treat- 

 ment which the problem of the causes of variation commonly 

 receives. Environmental change, chemical injury, differences in 

 food supply, in temperature, in moisture, or the like have been 

 proposed as "causes." Admitting as we must do, that changes 

 may be produced — usually inhibitions of development — by sub- 

 jecting living things to changes in these respects, how can we 

 suppose it in the smallest degree likely that very precise, new, 

 and adaptative powers can be conferred on the germs by such 

 treatment? Reports of positive genetic consequences observed 

 comparable with those I have mentioned, become from time to 

 time current. We should I think regard them with the gravest 

 doubt. Few, so far as I am aware, have ever been confirmed, 

 though clear and repeated confirmation should be demanded 

 before we suffer ourselves at all to build upon such evidence. 

 In a subsequent chapter some of these cases will be considered in 

 detail. 



In no class of cases would the transmission of an acquired 

 character superficially appear so probable as in those where power 

 of resisting the attack of a pathogenic organism is acquired in 

 the lifetime of the zygote. The possession of such a power is 

 moreover a distinction comparable with those which differentiate 

 varieties and species. It is due to the development in the blood 

 of specific substances which pervade the whole fluid. This 

 development is exactly one of those "appropriate responses to 



