352 COMPARATIVE PHYSIOLOGY. 



tissue-lymph, it is not a mere effusion with which the tissues, 

 for which it is provided, have nothing to do. The differences 

 may be beyond our chemistry to determine, but to assume that 

 all lymph poured out is alike is too crude a conception to meet 

 the facts of the case. Glands, too, it will be remembered, derive 

 their materials, like all other tissues, not directly from the 

 blood, but from the lymph. We, believe that the cells of the 

 capillaries, like all others, are influenced by the nervous system, 

 notwithstanding that nerves have not been traced terminating 

 in them. 



It is to be borne in mind that the lymph, like the blood, 

 receives tissue waste-products — in fact, it is very important to 

 realize that the lymph is, in the first instance, a sort of better 

 blood — an improved, selected material, so far as any tissue is 

 concerned, which becomes gradually deteriorated. 



We have not the space to give all the reasons on which the 

 opinions expressed above are founded; but, if the student has 

 become imbued with the principles that pervade this work thus 

 far, he will be prepared for the attitude we have taken, and 

 sympathize with our departures from the mechanical (physical) 

 physiology. 



We think it would be a great gain for physiology if the use 

 of the term " absorption," as applied to the alimentary tract, 

 were given up altogether, as it is sure to lead to the substitu- 

 tion of the gross conceptions of physical processes instead of 

 the subtle though at present rather indefinite ideas of vital 

 processes. We prefer ignorance to narrow, artificial, and er- 

 roneous views. 



Pathological.— Under certain circumstances, of which one is 

 obstruction to the venous circulation or the lymphatics, fluid 

 may be poured out or effused into the neighboring tissues or the 

 serous cavities. This is of very variable composition, but always 

 contains enough salts and proteids to remind one of the blood. 



Such fluids are often spoken of as '"lymph," though the 

 resemblance to normal tissue-lymph is but of the crudest kind; 

 and the condition of the vessels when it is secreted, if such a 

 term is here appropriate, is not to be compared to the natural 

 separation of the normal lymph— in fact, were this not so, it 

 would be identical with the latter, which it is not. When such 

 effusions take place they are in themselves evidence of altered 

 (and not merely increased) function. 



The Fseces.— The faeces may be regarded in at least a three- 



