332 PHYSIOLOGY OF GROWTH AND CONFIGURATION 



nancy of the animal on which it was grafted, and even yielded milk at the end of 

 pregnancy. Starling's experiments and those of Lane-Claypon 1 have shown 

 that a special hormone, developed in the embryo and distributed through- 

 out the body of the mother, is involved in the case just described. These 

 workers succeeded in inducing the development of lactiferous glands in virgin 

 females of the rabbit by injecting an extract of the fcetus from a pregnant 

 female. The artificially produced gland was about as large as in the case 

 of a normal pregnant female at about the ninth or tenth day of pregnancy. 



The following quotation from Biedl 2 gives an idea of some modern concep- 

 tions concerning hormone action. "Today we find that the theory of internal 

 secretion plays an important part in nearly all the problems of physiology and 

 pathology and that it is very important in connection with general biological 

 problems. Nothing is more characteristic of the recent change of our attitude 

 toward the role of specific internal secretions than is Schiefferdecker's hypothesis 

 concerning the role of specific internal secretions in the control of the nervous 

 system. This hypothesis supposes that the influence upon other cells, exerted 

 by the metabolic products emanating from nerve cells during their ordinary 

 nutritive processes, is tropistic in nature, while the influence exerted by sub- 

 stances arising in nerve cells during their special activity is to be considered as a 

 stimulating one. These conceptions of the nature of nervous control are now 

 indeed, generally accepted, but they show very clearly how our attitude toward 

 nerve activity has changed in recent times. All correlations in activity between 

 organs used to be regarded as nervous phenomena, now nervous control is 

 regarded as of a chemical nature." 



Hormones probably occur also in plants, as well as in animals. 3 Even as 

 early a writer as Duhamel gave vague expression to the idea that various phe- 

 nomena of plant growth and development are not to be explained by reference 

 to external conditions alone, and Sachs elaborated this idea and expressed the 

 opinion that an explanation of many such phenomena must be sought inside the 

 plant itself. In a paper on the relation of material to the form and structure 

 of plant organs 4 this author expressed himself very definitely, stating that 

 "with a diversity in the form of organs goes a corresponding diversity in the 

 materials of which they are composed." Before Brown-Sequard and other 

 authors entered this field in animal physiology Sachs had written of organ- 

 forming materials (" Organbildende Stoffe"), and in his work concerning the 

 influence of ultra-violet rays upon the formation of flowers he wrote: "These 

 flower-forming substances act, like ferments, upon large masses of plastic 

 material, although they themselves are present in exceedingly small amounts." 



i Lane-Claypon, (Miss) J. E. ( and Starling, E. H., An experimental enquiry into the factors which 

 determine the growth and activity of the mammary glands. Proc. Roy. Soc. London B 77 : 505-522. 1906. 



2 Biedl, Arthur, Innere Sekretion. Ihre physiologische Grundlagen fur die Bedeutung fur die Patho- 

 logie. Berlin, 1910. P. 23. 



3 Massart, Jean, Essai de classification des reflexes non nerveux. Ann. Inst. Pasteur 15 : 635-072. 

 1001. [Idem, same title. Receuil Inst. Bot. Bruxelles 5: 299-345- 1901.] 



« Sachs, J., von, Stoff und Form der Pflanzenorgane. Arbeit Bot. Inst. Wurzburg 2 : 4S2-488, 689-718. 

 1882. 



5 Sachs, Julius, Ueber die Wirkung der ultravioletten Strahlen auf die Bliithenbildung. Arbeit. Bot. 

 Inst. Wurzburg 3: 372-388. 1887. Idem, Gesammelte Abhandlungen uber Pflanzenphysiologie 1: 307- 

 309. Leipzig, 1892.* 



