2IO Heredity and Eugenics 



germinal substance. MacDougal's general conclusion, as 

 to the manner of producing this result, is that the action of 

 the injected chemicals is to accelerate or retard processes, 

 especially those of a katalytic nature within the germ cells, 

 or possibly, actual chemical changes in germinal substance 

 may be affected. 



IN ANIMALS 



In animals the most satisfactory results have been 

 obtained with higher types, while among the lower t^'pes. 

 Protozoa, for example, changes by incident forces, though 

 capable of production, behave in much the same manner 

 as do changes induced in bacteria and yeasts. In some 

 instances, variations persist for many successive fissions, but 

 they usually occur in only one of the individuals of each pair, 

 as in Jennings' Paramoecium with a spine. In these in- 

 stances there is little or no spread of the change in the popu- 

 lation through reproduction and thus far no long-continued 

 strains have been developed through these agencies. The 

 condition of protozoans in the non-differentiation of soma 

 and germ, as in bacteria, is a complication not easily over- 

 come in experiment, and it may well be, as has been often 

 suggested, that the entire organism is the ''germ plasm." 



Attempts to produce germinal changes by the direct 

 action upon the germ of external agents have not been made 

 by many workers. Many, it is true, have subjected organ- 

 isms to changed conditions and obtained modifications, 

 aberrations, but relatively few tests have been made to 

 determine the inheritability of these changes. 



The recent experiments of Woltereck with Daphnia 

 and Sumner with mice are good examples of a common 

 t>'pe of investigation, Woltereck carried strains of Daphnia 

 in cultures in which over-feeding was practiced for about 



