i INTERNAL PROTECTIVE SECRETIONS 3 



finest terminal ramifications of these vessels (where no blood 

 corpuscles can penetrate) are in direct continuity with the origin 

 of the excretory ducts. 



Haller (1757) decided the controversy between Malpighi and 

 Ruysch in favour of the latter, and tried to re-establish the ancient 

 doctrine, by which the arteries terminate in the form of open 

 mouths, either in the excretory ducts, or in the so-called cellular 

 tissue, in the lymphatic sinuses, the skin, etc. The argument on 

 which he founded this unfortunate theory (which contradicted 

 Malpighi's discovery of the capillary vessels as a completely closed 

 system uniting the arteries with the veins) was the passage of 

 injection masses, as performed by Ruysch, from the blood vascular 

 system into the excretory ducts of the glands, and the haemorrhages 

 simultaneously observed in the excretory canals. Haller's 

 doctrine, based on imperfect morphological data, held its own for 

 many years, until it was overthrown by the masterly monograph 

 of Johannes Miiller, De glandularum secernentium structura 

 penitiori (Lipsiae, 1830). Miiller's wide anatomical and embryo- 

 logical observations on the various secretory organs found in the 

 different classes of vertebrates, laid the foundations of modern 

 glandular morphology, and from this he deduced the physiological 

 concepts of his classical treatise. Its most characteristic points 

 are briefly as follows : 



(a) Whatever differences of structure exist in the glands of 

 animals and man, they all obey the same laws, and present an 

 uninterrupted series from the simplest follicle to the most 

 complex gland. 



(&) All glands present internally a large secreting surface, 

 obtained in an immense variety of forms. In all, however, the 

 surface extension is due to development of the excretory ducts in 

 the form of internal cavities or blind canals, as held by Malpighi. 



(c) In all glands, the blood capillaries behave in respect to the 

 walls of the canals and extremities of the glands as to every other 

 thin secreting membrane. They do not open by orifices into the 

 secretory spaces or cavities, but form a close capillary network 

 round them, which unites the dendritic ramifications of the 

 arteries and veins, as held by Malpighi. 



(d) Secretion is only a particular mode of the metamorphoses 

 which the blood undergoes in circulating through the organs. 

 The most complicated gland is but a large surface adapted to 

 the smallest possible space, through which transformation of the 

 blood takes place. Secretion does not occur only at the ex- 

 tremity of the glandular ducts, in the 'acini, supposed hypo- 

 thetically to exist in every gland. Acini, in the sense of closed 

 vesicles, are present only in a very small number of glands. 

 Secretion takes place throughout the length of the glandular 

 canals. 



