710 



SCIENCE 



[N. S. YoL. XLI. No. 1063 



liutli showed that if the eye of a salamander 

 larva is transplanted into another larva the 

 transplanted eye undergoes its metamor- 

 phosis into the typical eye of the adult form 

 simultaneously with the normal eyes of the 

 individual into which it was transplanted. 

 These and other observations of a similar 

 character show that substances circulating 

 in the blood are responsible for the phe- 

 nomena of growth in this case. 



A very instructive observation on the 

 role of internal secretion on growth was 

 made by Leo Loeb. When the fertilized 

 ovum comes in contact with the wall of the 

 uterus it calls forth a growth there, namely, 

 the formation of the maternal placenta 

 (decidua). Leo Loeb showed that the cor- 

 pus luteum of the ovary gives off a sub- 

 stance to the blood which alters the tissues 

 in the uterus in such a way that any contact 

 with any foreign body induces this deci- 

 duoma formation. The case is of interest 

 since it indicates that the substance given 

 off by the corpus luteum does not induce 

 growth directly, but that it allows mechan- 

 ical contact with a foreign body to induce 

 growth, while without the intervention of 

 the corpus luteum substance no such effect 

 of the mechanical stimulus would be ob- 

 servable. The action of the substance of 

 the corpus luteum is independent of the 

 nervous system, since in a uterus which has 

 been cut out and retransplanted into the 

 animal the same phenomenon can be ob- 

 served. 



All these cases agree in this, that appar- 

 ently specific substances induce or favor 

 growth not in the whole body, but in spe- 

 cial parts of the body. This recalls the idea 

 of Sachs that there must be in each organ- 

 ism as many specific organ-forming sub- 

 stances as there are organs in the body. 

 When this statement was made by Sachs 

 the facts on the specific effect of internal 

 secretion were unknown. To-day we can 



say that Sachs's theory is certainly sup- 

 ported by a stately array of facts. 



There may also be substances which affect 

 growth more generally. This is indicated 

 in the apparent connection of acromegaly 

 and giantism with diseases of the hypo- 

 physis and in the inhibition of longitudinal 

 growth after extirpation of the thyroid. 



We are, however, unable to answer the 

 question as to how these substances induce 

 the cells to grow. Are the resting cells in 

 the body in the condition of the unfertil- 

 ized egg and does the thyroid in Guder- 

 natsch's experiment produce an alteration 

 of the cortical layer of the cells from which 

 the legs grow out, similar to that caused by 

 the butyric-acid treatment of the egg? It 

 would not be safe to make such an assump- 

 tion at present, since we do not even know 

 whether the products of internal secretion 

 act directly on the growing cell or only 'in 

 some indirect way. We only know that 

 conditions of rest in the cells may be inter- 

 rupted by the production of certain sub- 

 stances in the body or by their introdiic- 

 tion in the form of food ; and conversely we 

 may suspect that the rest of the cells may 

 have been enforced by the presence of 

 other substances (or cells) in the blood 

 antagonistic to the former. 



The idea that the products of internal 

 secretion or certain substances taken up in 

 the food do not act directly upon the cells 

 whose growth they influence, but indirectly 

 through an alteration of metabolism, is 

 strongly supported by the interesting ob- 

 servations of Geoffrey Smith. Claude Ber- 

 nard and Vitzou had shown that the pe- 

 riod of growth and moulting of the higher 

 Crustacea is accompanied by a heaping up 

 of glycogen in the liver and subdermal con- 

 nective tissue. Smith found that during 

 the period between two moultings when 

 there was no growth the storage cells are 

 seen to be filled with large and numerous 



