GENERAL CONSIDERATIONS. 159 



exhalents, often talked of, but as yet never seen? That the 

 lateral porosities of blood vessels are large enough to allow 

 watery fluids to exude, is readily proved by injecting water 

 into the blood vessels of a limb, or of any other part, when 'Hie 

 latter invariably becomes cedematous. It is in this way even 

 possible to inundate a living animal, as I have seen accomplished 

 by M. Magendie, in Paris. This moisture requires a change, 

 and by continued additions would become superabundant: as it 

 has been thrown out of the common current of the circulation 

 and could not be removed in any other way, the lymphatic sys- 

 tem has, therefore, been added for the purpose. In the lower 

 orders of animals, who are destitute of the blood vessels, the 

 interstitial change of moisture goes on without lymphatics, 



No part of the human body is exempt from moisture, but 

 it is furnished by smaller streams, and is also Jess abundant 

 in some textures than in others; for example, though blood 

 vessels susceptible of conveying red blood do ramify through 

 tendons and ligaments, yet they are not numerous, apparently; 

 not more so, indeed, than what is sufficient to keep up by a de- 

 posite of serum, the flexibility of those parts. The vascularity 

 of a part during life may be ascertained by a simple process 

 after death, the most vascular always lose proportionately of 

 their bulk by drying; for example, a muscle shrinks more than 

 a tendon, a gland more than a muscle. 



Besides the operation of the lymphatics, much of the super- 

 abundant moisture is carried oil' by insensible perspiration and 

 evaporation from the surface of the body: the latter process, 

 however, is much restrained by the peculiar character of the 

 cuticle, without which it would become excessive, probably 

 so much so as to exceed any supply of fluid through the 

 stomach. 



The red globules of the blood, besides their less obvious uses, 

 unquestionably serve to inspissate the serous or watery part, 

 by an intimate mixture with it, and thereby put a certain re- 

 straint upon its extravasation. They also, from their size, serve 

 to keep open the channels through which the blood circulates. 

 So much associated is the existence of red globules with regular 

 Mood vessels, that there are but few examples of animals having 



