ORGANIC SUBSTRATA OF THE ANIMAL ORGANISM. 27 



be separated into two wholly different classes, viz. progressive and 

 regressive metamorphosis of matter. However deserving these 

 words may be of being retained in physiological chemistry to serve 

 as concise and generalising designations, they do not express definite 

 ideas in relation to the abstruser study of this science, or of pure 

 zoo-chemistry. Without dwelling upon the fact that it is impos- 

 sible to prove, in the case of many zoo-chemical substances, 

 whether they belong to the progressive or the regressive meta- 

 morphosis of matter, we will only observe, that even in the animal 

 processes no limits can be drawn between the termination of pro- 

 gressive and the commencement of regressive metamorphosis. Car- 

 nivorous animals only introduce into their organism well-elaborated 

 animal matter, and hence in them the extent of the progressive 

 metamorphosis must be very inconsiderable; yet an opinion has 

 long been entertained, that in animal life there is a regressive 

 formation alone, and in vegetable life only a progressive develop- 

 ment of organic matter. The acrimonious discussion that arose, 

 as to whether the fibrin of the blood belonged to the progressive or 

 the regressive metamorphosis, is sufficient proof that no leading 

 principle is embodied to these terms. We perceive, therefore, that 

 a purely physiological mode of classification is as untenable as those 

 chemical methods which have been borrowed from the individual, 

 and, in most cases, incidental properties of substances. 



No chemist at all acquainted with the present state of organic 

 chemistry,, will be disposed to place such bodies as albumen and 

 urea in one genus, because both these substances are nitrogenous 

 and amphoteric, any more than the physiologist, who is well aware 

 that a nutrient substance must of necessity have a very different 

 chemical constitution from an excreted substance. We would, there- 

 fore, again observe that chemists and physiologists must perfectly 

 coincide in their views respecting the mode of classifying and 

 considering animal bodies, and that where they differ in their 

 description, both cannot be true to nature; for where, for instance, 

 a physiologist should regard a substance as a product of secretion, 

 while the chemist classed it with albuminous substances in accord- 

 ance with bis observation of its constitution, one or the other must 

 be in error ; since the chemical qualities of a body cannot be at 

 variance with the physiological. That method which fulfils the 

 requirements of both sciences, chemistry as well as physiology, 

 can therefore be the only correct mode of treating zoo-chemistry. 



Although zoo-chemistry constitutes the firmest basis of physio- 

 logical chemistry, and although the chemical element should be 



