Abderhalden and Rona1 have accomplished a most interesting experiment upon a dog. The animal was given daily a constant quantity of non-nitrogenous foods which were: fat, 25 grams; starch, 50 grams; cane-sugar, 10 grams; glucose, 5 grams. The dog was brought into nitrogen equilibrium by giving him meat containing 2 grams of nitrogen. Then for this were substituted the amino cleavage products of casein, produced by pancreatic digestion and also containing 2 grams of nitrogen. During sixteen days on this diet there was an average daily gain of o. 12 gram of nitrogen by the dog. Then casein hydrolized by acid and containing 2 grams of nitrogen was administered for ten days, during which time the dog lost 0.48 gram of nitrogen daily. Amino products prepared after this fashion will, therefore, not preserve nitrogen equihbrium. Lastly, the diet was continued without any nitrogenous food. The daily waste of body nitrogen was then 0.53 gram. The loss was the same as when the casein hydrolized by acid was ingested, indicating that this particular array of cleavage products had no protecting power over the body protein.

Henriques2 has hydrolized protein by digesting it with trypsin and erepsin and then treating with 20 per cent, sulphuric acid on the water-bath. The resulting material consists entirely of amino-acids with no admixture of poly-peptids, and if it still gives a pronounced tryptophan reaction it will support the organism in nitrogen equilibrium. In the absence of the single ammo-acid tryptophan, nitrogen equilibrium cannot be attained.

To complete the story, the work of Abderhalden3 must be recited. Nitrogen equilibrium and even nitrogen retention were established in a dog when the diet contained instead of protein the following mixture of pure amino-acids: Glycocoll 5 grams, d-alanin 10 grams, 1-serin 3 grams, 1-cystin 2 grams, d-valin 5 grams, 1-leucin 10 grams, d-isoleucin 5 grams, 1-aspartic acid 5 grams, d-glutamic acid 15 grams, 1-phenyl-alanin 5 grams, 1-tyrosin 5 grams, 1-lysin 5 grams, d-arginin 5 grams, 1-prolin 10 grams, 1-histidin 5 grams, and 1-tryptophan 5 grams. This mixture weighed 100 grams and contained 13.87 grams of nitrogen. It is not unlike ox muscle in relative composition (see p. 77).

1 Abderhalden and Rona: "Zeitschrift fur physiologische Chemie," 1905, xliv, 198.

2 Henriques: Ibid., 1907, liv, 406.

3 Abderhalden: "Zeitschr. f. physiol. Chem.," 1912, lxxvii, 22.

It is therefore proved that amino bodies resulting from certain proteolytic cleavages may be the equivalent in metabolism of ingested protein itself.

In practical dietetics these substances can have little value, as they tend to produce diarrhea, as do also albumoses and peptones when given in any considerable quantity.1 As illustrating this Cronheim2 finds that though "Somatose" is more digestible than meat, still over 30 grams are undesirable in the daily diet of a man.

It is certain that if there be a new construction of protein in the body from the amino-acids formed in digestion such new proteins are characteristic of the organism, and do not possess the properties of the proteins originally ingested. To illustrate this Abderhalden and Samuely3 gave to a horse 1500 grams of gliadin, a vegetable protein which contains 36.5 per cent, of glutamic acid. They wondered if the ingestion of such a protein would in any way modify the composition of the proteins of the blood-serum, of serum globulin which under ordinary circumstances contains 8.5 per cent., and of serum albumin which contains 7.7 per cent, of glutamic acid. Their results were as follows:

Influence Of Gliadin Ingestion On The Percentage Of Glutamic Acid In The Serum Proteins Of The Horse

1 Voit, F.: "Munchener med. Wochenschrift," 1899, xlvi, 172. 2 Cronheim: "Pfluger's Archiv," 1904, cvi, 17.

3Abderhalden and Samuely: "Zeitschrift fur physiologische Chemie," 1905, xlvi, 193.

It is evident that gliadin, which contains so large a proportion of glutamic acid, is without influence on the composition of the blood-serum. Abderhalden conceived that such proportions of. the amino-acids within the gliadin complex as are available for the formation of new serum albumin and serum globulin were used for the generation of these proteins. Evidence that amino-acids enter the blood-stream directly from the intestinal tract has already been submitted. Furthermore, Henriques and Anderson1 have administered continuous intravenous injections of meat hydrolized with trypsin and erepsin to goats which had survived the operation of extirpating the intestines, and have noted nitrogen retention. From this they conclude that the intestine is not necessary for protein regeneration.

It has already been stated (p. 74) that if the serum of a dog be injected into the blood-vessels of another dog the nitrogen of it will be eliminated in the urine. This is also true of proteins foreign to the organism, and these likewise act in a toxic manner to destroy body protein. Thus Mendel and Rock-wood2 have shown that if edestin, a pure crystalline protein prepared from hemp seed, be injected intravenously into a fasting dog, there is for two days a metabolism of protein which is much greater than that of former days plus that of the edestin administered. The same truth holds when casein is injected. Similar injection of horses' serum into dogs appears to have no toxic action (Rona and Michaelis3). This work is of interest in connection with the subject of anaphylaxis, called also the Theobald Smith phenomenon, which has been especially investigated by Rosenau and Anderson. Injections of a protein foreign to the organism render the body sensitive to a second injection of the same protein. Large or small amounts of foreign protein may be injected in the first instance without intoxication, but if the animal be once "sensitized" a small amount of the same protein will terminate the animal's existence. It has recently been stated by Wells1 that the injection of so minimal an amount as 1/1000000 gram of pure crystalline egg-albumin will "sensitize" a guinea-pig so that a subsequent injection into the blood of 1/10 milligram of the same substance is lethal, although such a dose given in the first instance would not have injured the animal. It is evident, therefore, that the alimentary canal cannot allow the passage of proteins without changing them. This also explains the complete immunity of the organism to snake venom which has been swallowed.

1 Henriques and Anderson: "Zeitschrift fur physiologische Chemie," 1914, xcii, 194.

2 Mendel and Rockwood: "American Journal of Physiology," 1904, xii, 350.

3 Rona and Michaelis: "Pfluger's Archiv," 1908, cxxi, 163; 1908, cxxiii, 406.