DIVISION RATE IN CILIATE PROTOZOA AS 

 INFLUENCED BY THYROID CONSTITUENTS.^ 



robert a. budington and helen f. harvey. 



Introduction. 



In the very numerous studies which have been made to ascer- 

 tain the effect of thyroid tissues and extracts on growth and 

 differentiation, the material employed, whether used as a food 

 for large organisms or as a component of a medium in which to 

 breed smaller forms, has been taken in a very large proportion 

 of instances, if not always, from some mammal, e. g., cow, horse, 

 or sheep. This has been the case even though the animal under 

 observation may have been a mammal, a bird, an amphibian, 

 or a protozoan. 



Assuming that the doctrine of evolution is a fairly probable 

 hypothesis it is only a natural if not necessary corollary that 

 each of the several organs involved, as well as the organism as a 

 whole, has experienced its own successive changes, its own evo- 

 lutionary modifications. Variations, "continuous" and "dis- 

 continuous," have occurred in internal as well as in external 

 organs, and these variations have involved the physiological 

 value of the organs concerned, as well as their anatomy; so that, 

 of glandular tissues, for example, the composition of the output 

 has undergone phylogenetic changes, so to speak, during the 

 process of descent of one phylum from another. It is a priori 

 improbable, of course, that the chemical composition, and conse- 

 quent stimulating potency, of the thyroid secretion is the same 

 throughout the entire vertebrate phylum. 



Apparently the earliest experimentation along the line with 

 which this paper deals was carried out by Nowikoff ('08), who 

 found that one effect of putting sheep thyroid into the medium 

 in which Paramoecium was living was to cause it to divide more 

 rapidly than normally. 



Recently, Shumway ('14) has published a paper in which he 

 verifies Nowikoff's contentions. Both these investigators, how- 

 ever, employed mammalian thyroid; and, since our results agree 



' From the Department of Zoology, Oberlin College. 



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