Turning next to Pflüger’s[51] views regarding proteid katabolism, we find a totally different outlook. Here, the supposition prevails that the plasma of the blood and lymph, with its contained proteid, is the food of the organs or their cells, but that before this food material can undergo katabolism it must first be absorbed by the cell and built up into the living protoplasm of the tissue. In other words, according to the views expressed by Pflüger, katabolism must be preceded by organization of the proteid. Expressed in still different language, the proteid material circulating in blood and lymph must be eaten up by the hungry cells and, by appropriate anabolic processes, made an integral part of the living protoplasm before disassimilation can occur. Further, according to Pflüger’s conception of these processes, there is a radical difference in the chemical nature of living protoplasm as compared with that of the so-called circulating proteid. The latter is looked upon as being comparatively stable, resisting oxidation in high degree, and hence not prone to undergo metabolism. Living protoplasm, on the other hand, is characterized by instability, suffering oxidation with the greatest ease, and hence readily broken down in the ordinary processes of katabolism. Assuming for the moment the correctness of this theory, we see at a glance that all disruption of proteid matter in the body must be preceded by the upbuilding of the proteid into living protoplasm. There can be no destruction of proteid until the latter has been raised to the high plane of living matter. The dead, inert circulating proteid can serve simply as food for the living cells, and cannot undergo katabolism until it has been built up into the organized structure of the tissue or organ. Even though we grant that a small proportion of proteid may suffer katabolism without previous organization, it does not materially modify the general trend of the argument that, according to Pflüger’s hypothesis, proteid katabolism is essentially a process involving the disruption of living protoplasm. [51] Eduard Pflüger: Ueber einige Gesetze des Eiweissstoffwechsels (mit besonderer Berücksichtigung der Lehre vom sogenannten “circulirenden Eiweiss”). Archiv f. d. gesammte Physiologie, Band 54, p. 333.