2 ANNALES DE L'INSTITUT PASTEUR 



Ihe growth of shoots from buds, and if llie root is eut o(î, Ihe 

 colleition of Ihc doscending sap at the base will indiice there 

 the growth of roots. Sachs accepted thnse views and genera- 

 lized thcm by assuming as many différent spécifie organ- 

 forming substances in Ihe plant (or animal) as there are organs. 

 Thèse spécifie substances were said to be présent in minute 

 quantilies only. This assumption bas received some support 

 by récent observations on the elfect of internai sécrétions^ 

 espeeially the thyroid gland. 



In bis early experiments on régénération and heteromor- 

 phosis in animais the vvriter was able to point out that the 

 chemical viewpoint of Bonnet, Duhamel and Sachs harmo- 

 nized very well with his observations. Thus he had found 

 that if a pièce is eut from a stem of Tuhularia (a hydroid) and 

 suspended in sea waler, a head (hydranth) will form at either 

 end of the stem, but the head will form much more rapidly at 

 the oral than atthe aboral end of the pièce; the différence may 

 amount from a few days to a few weeks. Suppression of the 

 head formation at the oral end (by withdrawal of oxygen at 

 that end) accelerated the formation of the head at the aboral 

 end, so that the latter often formed as early as the oral head in 

 the pièces with normal oxygen supply. This is intelligible on 

 the assumption that the head formation is determined by sub- 

 stances which normally flow towards the oral end of an excised 

 pièce of stem until a head bas been formed, and that after- 

 vvards the direction of the flow is reversed; and that if the 

 formation of a head at the oral end is suppressed by the with- 

 drawal of oxygen at this end, the flow is reversed from the 

 beginning and a head can develop at the aboral end as rapidly 

 as the head at the oral end can under normal conditions. This 

 conclusion eould be submitted to a test by ligaturing an excised 

 pièce of stem of Tuhularia anywhere between the two ends. 

 This ligature should interrupt the flow of thehypothetical head- 

 forming substances from the aboral towards the oral end, and 

 hence should abolish the cause for the retardation of the head 

 formation at the aboral end ; and this was found to be true by 

 Godlewski as well as by the writer (1). 



(1) J. LoEn, La conception mécanique de la vie, Paris, 1914 et La dynamique 

 des phe'no?nhies de la vie, Paris, 1908 (libi'airie Félix Alcan). 



