GENERAL METABOLISM. 639 



become still more remarkable when we follow, as we have done, the behavior 

 of albumin in the animal organism. We find that in the alimentary canal 

 it undergoes a far-reaching decomposition. Now the different albumins 

 are very similarly constituted in respect to the amino acids which they 

 contain. With few exceptions they all contain the same building-stones. 

 Their chief difference lies in the relative amounts which they contain of 

 these acids. In spite of these differences the serum albumins are, as far 

 as our knowledge goes, of the same composition, no matter whether the 

 albumins contained in the food are closely related to the serum bodies 

 in their composition or not. 1 Although the researches in this direction 

 have only just begun, still a number of observations indicate that the 

 albumin in the food is so transformed before it reaches the circulation and 

 the tissues that it loses its original character and becomes of a nature 

 corresponding to the body albumins, first of all to the serum albumins. 

 It is, in fact, not the albumins of the food that circulate in the blood and 

 tissues, but rather those of the body itself. 2 Possibly, if we were able to 

 trace more closely the transformations of the albumias on their path of 

 absorption and assimilation, and had a better understanding of the albu- 

 min molecule, the decompositions would then appear to be very simple 

 ones. At present it appears as if we could not neglect the above-described 

 relations in the conception of albumin metabolism. According to them, 

 the decomposition which albumin undergoes does not appear to be a rela- 

 tively simple process. It is certain that the albumin before it is consumed 

 must be decomposed again in the tissues into simpler components. The 

 great question is only with regard to the reason for the changes in the 

 albumin in the food, so that it becomes like the albumin of the body, when 

 it is to be consumed so quickly. 



It seems to us as if the answer to this question, as we have previously 

 stated, 3 will give the solution to the enigma of the large albumin require- 

 ment. To be sure, the animal organism effects all these changes chiefly 

 in order that nourishment may be offered to the cells in a form such 

 that they are able to utilize it. We must always remember that the cells 

 eventually accomplish their work by means of ferments, and that these are 

 regulated very sensitively so that they will react only with certain definitely 

 constituted compounds. Undoubtedly the tissue-cells cannot break down 

 and utilize starch, or the fat and albumin of the food. The intestine 

 works over these materials and gives to the cells nutriment of quite specific 

 composition. The cells are capable of utilizing these definite products and 

 only these. Their whole construction corresponds to these compounds. 



1 Emil Abderhalden and Franz Samuely: Z. physiol. Chem. 46, 193 (1905). 



2 In Lecture XXIX we shall discuss a biological method for determining whether 

 the albumin nutriment passes directly into the blood and lymph circulation. 



3 Cf. Lecture XI, p. 223 et seq. 



