jga PHYSIOLOGY OF GROWTH AND CONFIGURATION 



tended vertically in a moist chamber, some of them being inverted, so that the 

 ;nd that was originally toward the root (the root-pole) is now uppermost The 

 jpright pieces form roots at the lower end and leafy shoots at the upper, while 

 ;he inverted pieces develop only roots at the upper end — where these organs 

 seem to be teleogically useless — and only branches at the lower end (Fig. 170). 

 [t thus appears that each piece of willow stem possesses two poles, a root-pole 

 md a shoot-pole, and the tissues near each pole always produce the kind of 

 jrgan characteristic of that particular pole, without reference to external con- 

 iitions, such as gravitation, light, etc. 



The mutual influence of various organs and their peculiar and seemingly 

 purposeful activities in the developmental process — in fact, all that is imphed 

 ^n the term consensus pa? Hum — have long constituted an enigma in physiological 

 science. In animals, the regulating activities by which the correlation between 

 different organs and tissues are brought about have been, until recently, ascribed 

 to the nervous system, but it is now known that there are special substances 

 that control the activities of the different organs and even bring about the 

 development of new organs. Each of these substances is formed in some 

 special part of the organism and is then transferred to other parts, which may 

 be at a great distance, and it may there induce various kinds of chemical reactions. 

 Starling' has introduced the term hormone for this kind of substance, which 

 acts, as it were, like a chemical messenger. The effect of the development of one 

 jrgan upon that of another was emphasized, for the animal organism, by Brown- 

 Sequard, who showed that there is a chemical substance in the testes of the male 

 that affects the whole condition and even the mentality of the organism. His 

 conclusioris concerning the influence of these substances are embodied in the 

 following quotations. " Je crois encore qu'fl est parfaitement possible de reparer 

 les ans les outrages reparables."^ "Les testicules donnent a I'homme ses plus 

 aobles et ses plus utfles attributs." (Brown-Sequard, 1889, page 652.) 



Substances are produced in the testes by internal secretion, and these, 

 being distributed through the body, occasion many of the pronounced differ- 

 snces between male and female animals. . There are many illustrations of 

 hormone action in animal physiology, of which a single instance may be referred 

 to in detail here, the relation between pregnancy and the development of the 

 actiferous glands. Ribbert' grafted a mammary gland from one animal on to 

 mother feitiale, near the ear, and the grafted gland enlarged during the preg- 

 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* have shown 

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

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



1 starling, E. H., The Croonian Lectures on the chemical correlation of the functions of the body- 

 l^ancet 169: 339-341. 423-42.I. SOI-S03, 579-583. 1905. Bayliss and Starling, 1906. [See note 2, p- 

 155-1 ,. , 



2 Brown-Sfiquard, 0. E., Experience dimonstrant la puissance dynamogenique chez Thomme d'un liquids 

 5xtrait de testicules d'animaux. Arch, physiol. i : 651-658. 1889. 



.'Ribbert, Hugo, Ueber Transplantation von Ovarium. Hoden und Mamma. Arch. Entwickelungs- 

 mech. der Organismen 7 : 688-708. 1898. 



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

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



