208 METAMORPHOSIS OF TISSUE. 



template the gretit series of the chemical substrata of the animal 

 body, we at once perceive that there are four principal groups of 

 substances in which the vital processes are manifested with the 

 greatest intensity. Amongst these the albuminous substances or 

 the so-called protein-bodies, and their derivatives are the most 

 conspicuous. A mere superficial glance at the occurrence of albu- 

 men is sufficient to show that this must be one of the most 

 important substances in the whole animal body; we have met 

 with it in the largest quantity in the blood, and in all those animal 

 juices which contribute directly towards the nutrition of the 

 organs, and a more careful examination of many of the animal 

 tissues shows that albumen requires only some very slight modifi- 

 cations to become consolidated under different forms; as, for 

 instance, when it contributes towards the formation of the solid 

 contractile parts, under the form of syntonin (muscle-fibrin), by 

 which alone, both the voluntary and involuntary movements of the 

 animal body are effected. We found it both in a dissolved and an 

 undissolved form in the most delicate organic combinations, as, for 

 instance, in the contents of the nerve-tubes structures by which 

 the animal essentially differs from the plant, and in which the 

 highest force of all animal life may be said to be located. While we 

 are compelled to admit that chemistry is still unable to furnish the 

 long looked-for explanation of the internal constitution of albumen 

 and of the substances most nearly allied to it, as syntonin, fibrin, 

 and casein, or to trace the numerous morphological metamor- 

 phoses to which they are subjected, we are still less able to answer 

 the question, wherein lies the capacity of these substances to preside 

 over the highest functions of life. As long as the chemical ques- 

 tions regarding the difference of albuminous substances of identical 

 or similar composition remain undetermined, we have no imme- 

 diate prospect of solving the physiological problem of what it is 

 which capacitates these substances for different vital functions. 



We find that the animal germ is surrounded by albumen and 

 casein, containing salts, together with a little fat and traces of 

 sugar ; hence it is to the albuminous contents of the egg that we 

 must refer the development of the organs of animals, including 

 even those structures whose substances do not appear very similar 

 to albumen. Animals obtain during the period of lactation, besides 

 fat and sugar, a substance which, with the exception of a smaller 

 amount of sulphur, contains the same elements, and in the same 

 proportions, as albumen ; at the period, therefore, when the 

 growth of the gelatigenous, non-albuminous tissues requires the 

 largest supplies from without, the body is supported by the same 



