FEEDING EXPERIMENTS WITH ABIURET PRODUCTS 43 



considered a protein sparer in dogs. Mauthner (277) also tested as- 

 paragine as a protein sparer on the dog, but without decisive result. 

 On the whole, he inclined to the belief that there was evidence of a 

 limited sparing action. 



As regards the herbivora asparagine is claimed by many workers 

 to be a very efficient protein sparer (Weiske, 418). Voltz (414) main- 

 tained that amide bodies could replace about two-thirds of the protein 

 in the food of adult ruminants. He concluded that, in all probability, 

 the herbivorous organism could build up its highly complex protein 

 out of a comparatively limited selection of amide bodies. The figures 

 given, if not absolutely convincing, are of great interest. Von Strusie- 

 wicz (389) also showed that sheep could have a very large proportion 

 of the protein in their diet replaced by amide nitrogen. 



On the other hand, there is much contrary experimental evidence 

 to the retention of nitrogen in animals fed on asparagine as their 

 source of nitrogen. Politis (333) could not obtain any evidence of the 

 protein sparing power of asparagine, when this substance was fed to 

 rats as the sole source of nitrogen, with an otherwise abundant diet, and 

 the same result was obtained by Henriques and Hansen (189). These 

 workers found, however, that although amide substances obtained from 

 young growing plants conld not replace the nitrogen of the food, they 

 could exert to a limited extent a protein sparing action. 



In a very interesting paper on this question Kellner (219) pointed 

 out that the protein sparing action of asparagine could only be de- 

 monstrated on a protein free or protein poor diet. If it were given 

 with a diet rich in nitrogen there might even be a stimulation of the 

 nitrogen metabolism. He also observed the same sparing action of 

 ammonium acetate when in a protein poor but carbohydrate rich diet. 

 Lu'thje (269) demonstrated that it was impossible to keep rabbits alive 

 on an abundant carbohydrate diet when the sole source of nitrogen 

 was the protein free amide material obtained from fresh potatoes. 



Viewing the evidence as a \vhole it would appear that amides and 

 even certain ammonium salts are capable of replacing a certain 

 amount of protein in the diet, i.e. acting as protein sparers, but are 

 certainly not capable of replacing all the protein in the diet. The re- 

 sults of these experiments do not then contribute much towards the 

 elucidation of the question of the transformation of the amino acids. 

 It is always possible that even in those experiments in which the 

 amide was shown to have a marked sparing action that the positive 

 result was due to the presence of the essential substances in the 

 other protein material given. In the case of the ammonium salts 



