CHAP, vi.] OF LIVING LIQUIDS. 57 



We have now to describe the humours of the first order, the 

 humours constituent, living, those which may be regarded in 

 some sort as liquefied anatomical elements. These liquids, which 

 exist with supreme distinctness only in animals with complex 

 structure, furnished with circulating apparatus well denned, are 

 only two in number, the blood and the Lymph ; for we must con- 

 sider the chyle, that is to say, that ultimate product of digestion 

 circulating in the lymphatic vessels, a dependency of the lymph. 



The blood and the lymph are contained in circulatory systems, 

 ramified and inclosed in every direction. These circulatory systems 

 imprison the liquids which are formed in them, without, normally, 

 permitting them to break forth in mass. But across their walls 

 they leave an easy passage to many materials coming either from 

 the tissues, or from the ambient medium and to many others which 

 escape from the blood and the lymph, either to nourish the tissues, 

 or to be expelled as unworthy from the frontiers of the organism. 



This double movement of coming and going, of exchange of 

 materials, is effected simultaneously, like the nutritive assimila- 

 tion and disassimilation in the solid elements. In truth the 

 blood and the lymph are living liquids, in process of perpetual 

 renovation. Incessantly they are formed in the system of the 

 canals where they circulate without being destroyed. 



The vascular walls which contain the constituent liquids do 

 not seem notably to modify the chemical composition of the sub- 

 stances which traverse them. The part they play is especially 

 physical, osmotic. Therefrom it results that the blood and the 

 lymph borrow their constituent materials already formed from 

 an ambient medium, either from the grand cosmic medium, the air 

 for example, or from the organic medium, the tissues, the 

 myriads of anatomical elements which compose the body of the 

 superior animals. 



Considered as organised liquids, the constituent humours neces- 

 sarily contain immediate principles of the three classes ; but those 

 of the third class, the albuminoids of organic origin, not crystal- 

 lisable or coagulable, predominate therein. They are albumins 



