INTRODUCTION. 11 



closely connected -with the chemical constitution of each indivi- 

 dual tissue. We find, for instance, that the lower elementary 

 tissues, such as exert a mere physico-mechanical action, are 

 moistened by a fluid which scarcely differs from the serum of the 

 blood, and in general closely resembles the transudations described 

 in the second volume. On the other hand, the tissues which are 

 capable of a vital contraction, and, consequently, the fibre-cells 

 and muscular fibres, are surrounded by a fluid which is altogether 

 different from an ordinary transudation ; in the first place this 

 fluid is distinguished, in all contractile tissues without exception, 

 by the presence of a certain amount of free acid ; further, the 

 phosphates and potash-salts predominate here over the chlorides 

 and soda-salts (which preponderate in the transudations) ; and, 

 lastly, there occur in this fluid a number of substances which, 

 hitherto at least, have not been recognised in the blood and trans- 

 udations. It may probably depend upon the different modes of 

 action of the fibre-cells (in the contractile tissues and in smooth 

 muscles) and of the muscular fibres (in the striped muscles), that 

 the acid interstitial juice in the former case always contain casein 

 with albumen, whilst, in the latter case, it contains no casein, but 

 several other substances peculiar to itself alone. Unfortunately 

 these relations afford us as yet mere points of view from which we 

 may get glimpses of the connexion between the chemical compo- 

 sition and the function of the tissues, or at most a few new 

 advanced points from which we may hope by further investigations 

 to promote the physiology of the animal tissues. 



The preceding remarks will sufficiently elucidate the course 

 which we intend to pursue in treating of the chemical relations of 

 the animal elementary tissues. We first notice the micro-chemical 

 reactions. In the present very imperfect state of micro-chemistry 

 a logical arrangement and subdivision of these reagents is out of 

 the question, and hence their number is far greater than it would 

 otherwise be. Although many of these reagents act in a very 

 analogous manner, and others again do not yield very definite 

 results, we shall, nevertheless, mention them in detail, as we are 

 of opinion that in a rapidly advancing and comparatively new 

 department of science every fact, however unimportant, should be 

 retained, since we do not know what significance it may subse- 

 quently attain. Moreover, no accumulation of facts can do harm. 



Basing our remarks for the most part on the micro-chemical 

 reactions, we shall next proceed to the investigation of the chemical 

 properties and composition of the individual substances which may 



