60 APPENDIX, 



parietes of the vessels, are all porous ; it is only with respect to the extent and mag- 

 nitude of the pores that the question can be entertained. Those who contend for the 

 existence of separate and subordinate sets of capillary vessels cannot deny the exis- 

 tence of pores, for if they do not exist both on the surfaces and in the textures whence 

 these capillaries are supposed to originate, how could they obtain the fluids circulating 

 in them ? On the other hand, those who contend for the existence and functions of 

 pores cannot deny the existence of minute absorbents or lymphatics, for they can be 

 demonstrated, to a certain extent, as respects the minuter ramifications, and, in a satis- 

 factory manner, as regards the more considerable brandies. It appears to us that 

 both species of organization exist to a greater or less extent in different textures, and 

 secreting- organs. 



Each secreting viscus, is supplied with a distinct ganglion, plexus, or both ; these 

 preside over the secreting function, and the functions of some of these ganglia are in- 

 fluenced by the operations of the cerebro-spinal system ; as, for example, the secretion 

 of the lachrymal gland is increased by the influence which the nerves of the latter sys- 

 tem convey to the ganglion which supplies it, and is the chief source of its functions. 



Of Nutrition. 

 Note C. C. and S. 



As we have already seen, in the notes on the capillary system and on secretion, the 

 function of nutrition has been explained, by one class of Physiologists, by supposing 

 the existence of nutritive capillaries, and by another, by means of. organic pores, with 

 which they endow the capillary vessels circulating red blood, and to which they com- 

 mit the exhalent, secreting, and nutritive functions. The first of these hypotheses 

 supposes that nutrition takes place in minute colourless vessels, which proceed in a 

 more or less tortuous direction from the arterial capillaries, absorption proceeding 

 through the medium of a similar set of colourless vessels continuous with the former, 

 which run into the venous capillaries, and thus the nutritious molecules are always cir- 

 culating within colourless capillaries, which, with the nerves and larger capillaries, 

 constitute the basis of the different textures. 



Mascagni supposes that the arterial capillaries, at the point where they change into 

 veins, are provided with exhalent pores both for the purposes of secretion and nutri- 

 tion ; and that there every where exist the orifices of minute absorbent vessels, com- 

 ifciencing in the latter description of pores, in order to take up the nutritive molecules. 

 The elementary tissues consist, in his opinion, of the particular class of absorbent ves- 

 sels, which contain the molecules as long as they are a part of the textures, and which 

 by their union, lorm the most simple membranes. 



' These hypotheses do not differ very materially. Both contend for the existence of 

 very fine capillaries which attract the nutritive molecules, and contain them in a state 

 of progressive circulation, as long as they form constituents of the textures : these 

 molecules being afterwards carried onward in succession into the branches of the ab- 

 sorbent lymphatics and into the veins. In the first of these hypotheses, the nutricious 

 particles are supposed to circulate in the finest of the vessels proceeding from the ar- 

 terial capillaries ; in the second, the process is ascribed to the most minute radicles of 

 the absorbents ; but both agree in considering the molecules constituting the mass of 

 the textures to be contained in colourless vessels, and to be in a state of continual cir- 

 culation. 



The opinion of Bichat on this subject is somewhat different. According to him, 

 each molecule of these constituting 1 the textures of the body is placed between the 

 orifices of two vessels : one, a nutritive exhalent orifice, which has deposited the mole- 

 cule, the other a nutritive absorbent orifice about to absorb it. 



Prochaska, who conceives that the arterial capillaries are continued directly into 

 veins, considers that nutrition takes place, in consequence of the porosity of the ca- 

 pillaries, and of the general permeability of the substances constituting the mass of 

 the structures. M. Richerand espouses a similar opinion, but he seems to allow ail 

 organic property to the pores which lie ascribes to the capillary vessels. 



Opinions respecting the mechanism of nutrition, or the manner in which it takes 

 place, can only be theoretical. We have not the means of demonstrating the exis- 

 tence or non-existence of either the one or the other mode of organization contended 

 fov: each may of itself be sufficient to explain the phenomenon, as far as respects the 



