312 ROBERT A. BUDINGTON AND HELEN F, HARVEY. 



own experience. There is essential agreement between the 

 findings of Nowikoff , Shumway, and ourselves as to the constant 

 effect of thyroid ingredients in increasing the division rate of 

 protozoa beyond the normal, at least so far as Paramoscium is 

 concerned. 



The work of others, notably Gudernatsch ('12, '13), on the 

 feeding of amphibian embryos, seems to indicate that the effect 

 there observed is mainly one of acceleration of differentiation of 

 tissues in the growing organism ; at least this is the interpretation 

 given their findings. West ('14) has verified certain features of 

 Gudernatsch 's results. A similar betrayal of specialization in 

 function would, of course, not be possible within the limits of 

 a unicellular organism. It seems entirely probable, however, 

 that intra-cellular modifications of the Paramcecium protoplasm 

 does accompany its feeding upon and living in a medium which, 

 among other things, brings it hurriedly to its most crucial ex- 

 perience, self-division. The fact that rapid fission of thyroid-fed 

 Paramcecia is accompanied by their increased activity and trans- 

 parency, and by smaller size,^ indicates that very important in- 

 ternal modifications doubtless occur. Careful study of protozoa 

 exposed to exigencies of this sort should be made. 



If cell division in protozoa is to be compared with anything in 

 the life history of metazoa, it should certainly be considered be- 

 side the early development of the metazoan egg. If the egg has 

 already advanced to the proportions of an embryo or larva, and 

 the precocious differentiation of tissues and organs in such is 

 under consideration, the question arises: Is this differentiation 

 at all explained in the same terms as is protozoan cell division, 

 or does it involve the same basic factors? It seems to us that 

 this query may very possibly be answered in the afifirmative, for 

 the reason that the sprouting out of legs from the tadpole and 

 establishment of other organs characteristic of the adult, is surely 

 not due to mere unusual division of labor among the young 

 cells generally acting as little more than unit components of the 

 infant tadpole body; but that these latter have been provoked 

 (by thyroid ingredients?) to abnormally rapid division, probably 



1 Shumway mentions these alterations to occur in thryoid-fed Paramcecia, and 

 we have found such to be practically always observable. 



