574 OF SECRETION AND EXCRETION. 



by Miiller and succeeding inquirers, that the new growth consists of a mass of 

 cells; which, like the Vegetable Fungi, develop themselves with great rapidity; 

 and which destroy the surrounding tissues by their pressure, as well as by ab- 

 stracting from the Blood the nourishment which was destined for them. These 

 parasitic masses have a completely independent power of growth and reproduc- 

 tion; and they can be propagated by inoculation, which may convey into the 

 tissues of the animal operated on, the germs of the peculiar cells that constitute 

 the morbid growth, these soon developing themselves into a new mass. So it 

 may be by the diffusion of the germs produced in one part, through the whole 

 fabric, by means of the circulating current, that the tendency to re-appearance 

 (which is one great feature in the malignant character of these diseases) is oc- 

 casioned. But it would seem more probable that this character rather depends 

 upon the presence of a morbid matter in the blood, of which the formation of 

 the cancerous tissue is only the manifestation ( 120); the local disease thus 

 being the consequence of a constitutional cachexia, rather than the constitu- 

 tional affection the result of the local disease. 1 



CHAPTER XII. 



OF SECRETION AND EXCRETION. 

 | 



1. Of Secretion in General. 



617. THE literal meaning of the term Secretion is separation; and this is 

 nearly its true acceptation in Physiology. But the ordinary processes of Nutri- 

 tion involve a separation of certain of the components of the Blood, which are 

 withdrawn from it by the appropriating power of the solid textures; and every 

 such removal may be considered in the light of an act of excretion, so far as the 

 blood and the rest of the organism are concerned ( 202). Moreover, the sepa- 

 ration of certain matters from the blood in a fluid state, either for the purpose of 

 being cast forth from the body, or of being employed for some special -purpose 

 within it, which constitutes what is ordinarily known as Secretion, is effected by 

 an agency of the same nature with that whose operation constitutes the essential 

 part of the nutritive process ; namely, the production and growth of cells. Hence 

 there is no other fundamental difference between the two processes, than such 

 as arises out of the diverse destinations of the separated matters, and the anatomi- 

 cal arrangements which respect- 

 Fig. 147. ively minister to these. For 



the products of the secreting ac- 

 tion are all poured forth either 

 upon the external surface of 

 the body, or upon the lining of 

 some of the cavities which com- 

 municatewith it; and the cells 

 by which they are separated 



Plan to show augmentation of surface by formation of pro- from ^ y^ uguall ^^ 

 cesses ; a, basement-membrane ; p. epithelial layer of secreting . i / A i 

 cells; c, layer of capillary vessels; d, simple processes; e, f, m the relation of epithelium- 

 branched or subdivided processes. cells to those prolongations of 



1 See Dr. Walshe on "The Nature and Treatment of Cancer ;" and Mr. Simon's " Gene- 

 ral Pathology," Lect. vin., Am. Ed. 



