150 CIRCULATING FLUIDS: 



albuminous tissues. If we regard the extractive matters as the 

 products of the nutrition and waste of the different tissues, the 

 variety in which they exhibit themselves is not at variance 

 with the conceptions we are led to form respecting the nature 

 of metamorphosis. Another circumstance in support of this 

 view is, that the formation of similar matters is observed in the 

 vegetable kingdom, where there is a vital, reciprocal action be- 

 tween the cells and the nutriment, combined either with the 

 production of lactic, or of some allied acid. Although these 

 extractive matters are, without doubt, entii'ely different from 

 those that occur in the animal body, they correspond in many 

 of their physical and chemical properties : both are inca- 

 pable of being exhibited in a crystalline form, they dissolve 

 readily in water and partially in alcohol, they are precipitated 

 by many of the metallic oxides, and it is a matter of extreme 

 difficulty to obtain them in a state of purity in consequence of 

 their tendency to undergo transformation and to become che- 

 mically changed. 



Until the extractive matters of the animal body have been 

 accurately analysed, and the composition of the various tissues 

 has been determined, it will be impossible to obtain a rational 

 insight into the nature of these changes. 



It appears from the statements of Berzelius, as well as from 

 my own investigations, that some of the extractive matters 

 which occur in the blood and in the flesh are also met with in 

 the urine. It still remains to be decided whether all the ex- 

 tractive matters of the flesh pass unchanged into the blood and 

 are thrown off by the urine, or whether they become changed 

 in their passage ; or, lastly, whether they are not partially me- 

 tamorphosed in certain organs, and again rendered fit to serve 

 the purposes of nutrition. When Ave consider the wisdom that 

 is universally obvious in the economy of the animal body, it 

 seems probable that the last is the most correct view, and it 

 is by no means improbable that the gelatinous tissues are sus- 

 tained by a cytoblastema, allied to the extractive matters. 

 The fact that some of the extractive matters of flesh are not 

 only strengthening but very digestible, renders it more than 

 probable that some of the matters of this class serve as nou- 

 rishment; while others, incompatible with the purposes of nu- 

 trition, are excreted. 



